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GEOLOGICAL   STUDIES; 

OR, 
ELEMENTS  OF  GEOLOGY. 

FOR 

HIGH  SCHOOLS,  COLLEGES,  NORMAL,  AND  OTHER  SCHOOLS 


PART  I.— GEOLOGY  INDUCTIVELY  PRESENTED. 
PART  II. —  GEOLOGY  TREATED  SYSTEMATICALLY. 


WITH  mi  ILLUSTRATIONS  IN  THE  TEXT. 


BY   ALEXANDER  WINCHELL,   LL.D. 

PROFESSOR  OF  GEOLOGY    AND   PALEONTOLOGY    IN    THE    UNIVERSITY    OF    MICHIGAN,  FOR- 
MERLY   DIRECTOR  OF  THE    GEOLOGICAL    SURVEY    OF   MICHIGAN,   AUTHOR  OF 
"  GEOLOGICAL  EXCURSIONS,"   FOR  ELEMENTARY  SCHOOLS,   ALSO 
OF    "SKETCHES    OF    CREATION,"     "WORLD     LIFE," 
ETC.,    ETC. 


CHICAGO: 
S.    C.    GRIGGS    AND    COMPANY. 

1886. 


COPYRIGHT,  1886, 
BY  S.  C.  GRIGGS  AND  COMPANY. 


I     KKIGHT    £c  LEONARD  .  I 
'  ' 


"THE  diffusion  of  that  which  is  specially  named  science  has  at  the  same 
time  spread  abroad  the  only  spirit  in  which  any  kind  of  knowledge  can  be 
prosecuted  to  a  result  of  lasting  intellectual  value." — PROFESSOR  JEBB. 

"All  the  subjects  which  the  sixteenth  century  decided  were  'liberal'  are 
studies  in  books;  but  natural  science  is  to  be  studied  not  in  books,  but  in 
things." — PRESIDENT  ELIOT. 

"The  genesis  of  knowledge  in  the  individual  must  follow  the  same  course 
as  the  genesis  of  knowledge  in  the  race." 

"Every  study  should  have  a  purely  experimental  introduction."— HER- 
BERT SPENCER. 

"Were  I  dictator,  I  would  drive  all  teachers  of  science  out  into  the  great 
field  of  dead  work;  force  them  to  go  through  all  the  gymnastics  of  original 
research  and  its  description,  and  not  permit  them  to  return  to  their  libraries 
until  their  note  books  were  full  of  their  own  measurements  and  calculations, 
sketch  maps,  and  farm  drawings,  severely  accurate,  and  logically  classified, 
to  be  then  compared  with  those  recorded  in  the  books."— JOSEPH  P.  LESLEY. 


258254 


PEEFAOE. 


THIS  work  on  the  elements  of  geology  is  intended  as  a  guide 
in  the  observation  of  nature,  and  a  synoptical  record  of  the 
more  important  facts  and  doctrines  of  the  science.  The  reader 
is  supposed  to  be  desirous  of  laying  substantial  foundations  for  a 
geological  education,  and  to  have  attained  such  mental  develop- 
ment as  to  require  a  text  book  more  advanced  than  the  Author's 
"Geological  Excursions."  The  method,  as  in  that  work,  is  an 
appeal  to  the  powers  of  observation;  and  the  facts  cited  are  the 
most  familiar  and  most  accessible.  Happily,  the  widespread 
Drift  of  the  northern  portion  of  the  continent  brings  to  nearly 
every  student's  door  a  body  of  phenomena  so  similar  as  to  supply 
an  intelligible  common  starting  point  for  a  very  large  proportion 
of  the  United  States  and  Canada;  while  for  students  of  the 
southern  states,  any  inconveniences  may  be  easily  overcome. 
Though  this  method  is  believed  to  be  unique,  it  is,  without  ques- 
tion, the  method  which  best  comports  with  the  order  of  develop- 
ment of  the  mental  faculties,  and  must  prove  most  easy  and 
gratifying  to  the  student.  It  is  the  application  to  geology  of 
those  sound  principles  which  have  come  into  vogue  among  the 
best  modern  teachers  of  the  other  sciences  of  nature.  That  it  is 
entirely  practicable  is  shown  by  the  personal  experience  of  the 
Author,  and  of  many  other  teachers  who  have  used  the  more 
rudimental  work  above  mentioned. 

What  there  is  among  the  universal  phenomena  of  the  Drift  to 
serve  as  the  elementary  data  of  geological  science  will  perhaps  be 
best  understood  by  turning  over  the  earlier  pages  of  the  First 
Part  of  the  book.  The  Author  does  not,  however,  imagine  the 
pupil  a  mere  recording  instrument;  but  bears  in  mind  the  fact 
that  the  dawn  of  reflection  is  simultaneous  with  the  exercise  of 


VI  PREFACE. 

perception.  The  observer  begins  immediately  to  group  phe- 
nomena—  to  generalize,  and  to  inquire  after  those  uniform 
antecedents  which  science  denominates  causes.  The  Author 
encourages  this  tendency  by  pausing  occasionally  to  review,  to 
summarize,  to  induce  a  general  principle,  and  even  to  theorize  a 
little.  Thus,  in  the  First  Part,  scientific  method  is  unknown. 
The  science  is  growing  up  in  the  learner's  mind  simultaneously 
and  symmetrically  in  all  its  departments,  just  as  it  grew  in  the 
intelligence  of  mankind. 

A  little  later,  after  the  nearest  phenomena  have  yielded  their 
lessons,  the  learner  is  led  from  home  to  widen  his  observations. 
Well,  indeed,  if  the  travel  can  be  real,  like  the  earlier  excursions 
into  the  neighborhood.  But  the  impracticability  of  this,  as  a 
rule,  is  offset,  as  far  as  possible,  by  graphical  illustrations.  In 
many  cases,  it  may  be  further  offset  by  specimens,  models,  and 
diagrams.  These  the  school,  or  the  teacher,  or  even  the  pupil 
himself,  may,  to  some  extent,  provide.  As,  after  all,  many 
things  can  only  be  known  from  descriptions,  the  effort  has  been 
made  to  have  them  intelligible. 

The  purpose  to  begin  with  the  Drift  has  led  to  a  more  careful 
study  of  common  minerals  and  rocks  than  has  heretofore  been 
undertaken  in  elementary  works;  but  this  feature,  the  Author 
believes,  requires  no  defence.  On  the  contrary,  he  is  already 
assured  that  the  tables  provided  for  determinations  of  minerals 
and  rocks  from  their  most  obvious  characters  will  receive  a  hearty 
welcome;  and  will  satisfy  many  longings  to  know  something 
more  about  the  objects  which  are  absolutely  the  most  obtrusive 
and  familiar  which  we  encounter. 

The  same  purpose  has  led  to  a  more  particular  study  of  some 
common  types  of  fossils  than  has  ordinarily  been  thought  appro- 
priate. But  this  study  has  been  restricted  mainly  to  examples 
widely  distributed  in  the  Drift,  and  therefore  generally  obtaina- 
ble; and  it  has  been  pursued  only  far  enough  to  illustrate  how  to 
study  fossils  in  a  scientific  way. 

The  outcome  of  the  First  Part  is  a  somewhat  chaotic  and 
undigested  mass  of  facts  and  doctrines,  buried  in  a  considerable 


PREFACE.  vii 

volume  of  verbiage.  It  does  not,  assuredly,  supply  the  means 
for  a  methodized  apprehension  of  the  elements  of  the  subject. 
But  it  supplies  many  fundamental  facts,  many  great  principles, 
many  impressions,  many  hints  for  personal  observation,  and  many 
impulses  to  continue.  Far  better  for  the  student  to  get  so  much 
than  to  leave  school  in  total  ignorance  of  a  science  which  sus- 
tains so  important  relations  to  industries,  to  culture,  and  to  civili- 
zation. 

Part  II  is  the  complement  of  this.  Here  the  whole  body  of 
facts  and  principles  is  reduced  to  methodical  re-presentation; 
though  the  necessity  of  abridgment  has  led,  in  some  of  the 
chapters,  to  mere  references  to  the  First  Part,  instead  of  recast- 
ings  of  the  matter.  Here,  too,  the  discussions  of  the  several 
topics  are  completed,  and  the  various  portions  are  adjusted  to  a 
logical  relation.  The  last  chapter  is  a  rapid  historical  sweep  over 
the  whole  range  of  terrestrial  events.  To  a  limited  extent, 
therefore,  the  book  may  be  used  for  elementary  reference.  But 
it  must  not  by  any  means  be  conceived  as  intended  for  a  manual. 
The  method  of  a  manual  is  suited  only  for  advanced  students 
and  investigators.  A  very  different  method  is  demanded  by  be- 
ginners. This  is  only  to  a  limited  extent  even  a  "text  book." 
That  term  savors  of  an  educational  method  which  is  obsolete  and 
repugnant.  The  present  work  is  a  guide  to  the  study  of  nature, 
and  a  synopsis  of  the  elementary  facts  and  principles  of  geolog- 
ical science. 

Because  the  work  is  elementary,  it  has  been  restricted  almost 
wholly  to  American  geology.  But  no  well  beaten  path  has  been 
pursued.  The  recent  additions  to  our  knowledge  of  American 
geology  have  greatly  transformed  the  science,  and  the  subject 
has  to  be  treated  very  much  as  if  no  elementary  books  had  been 
written.  Recent  investigations  have  placed  us  in  possession  of  a 
large  body  of  information  about  the  remote  interior  and  the 
Pacific  slope,  and  the  vast  region  north  of  our  national  boundary. 
To  this  fresh  information  the  author  has  attempted  to  give  due 
attention.  It  will  be  found  a  feature  of  the  work,  that  it  sur- 
passes other  elementary  books  in  its  presentation  of  western 


Vlll  PREFACE. 

geology,  especially  in  its  great  features  and  its  great  historical 
facts. 

The  author's  obligations,  of  course,  lie  in  every  direction; 
they  are,  indeed,  too  many  to  enumerate.  But  the  effort  has 
been  made  to  draw  less  on  the  writers  of  text  books  than  on 
original  sources.  To  his  publishers,  his  indebtedness  and  that  of 
the  public  is  great,  for  that  intelligent  liberality  which  has 
prompted  them  to  demand,  regardless  of  cost,  the  best  style  of 
graphic  illustration,  and  a  perfection  of  mechanical  execution 
which  will  scarcely  be  found  surpassed. 

The  author  entertains  the  hope  that  he  has  here  brought 
within  reach  of  his  fellow-workers  in  the  advancement  of  popu- 
lar education  some  improved  means  for  placing  geological  study 
where  of  right  it  belongs  —  side  by  side  with  the  most  esteemed 
and  most  favored  agencies  of  material  prosperity,  of  civilization, 
and  of  culture. 

UNIVERSITY  OF  MICHIGAN, 
ANN  ARBOR,  June,  1886. 


CONTENTS. 


PART   I.— FIELD    STUDIES; 

OR,  INDUCTIVE  GEOLOGY. 
How  WE  MAY  OBSERVE  THE  FACTS,  AND  LEARN  THEIR  MEANING 

STUDY  I.     SURFACE  MATERIALS, 1 

STUDY  II.     SPRINGS  AND  WELLS,    . 7 

STUDY  III.     BOWLDERS, 12 

STUDY  IV.     A  LITTLE  CHEMISTRY, 18 

STUDY  V.     QUARTZ  AND  FELDSPAR,        .         .         .         .     .    .         .23 

STUDY  VI.     DARK  COLORED  MINERALS,           .  29 
The  Micas  and  lamellar  species;  Araphibole,  Py- 
roxene, Hypersthene. 

STUDY  VII.     LIME,  MAGNESIA,  AND  IRON  MINERALS,      ...  34 
Calcite,  Dolomite,  Gypsum,  Haematite,  Magnetite. 

STUDY  VIII.     REVIEW  OF  THE  IMPORTANT  MINERALS,      ...  39 

Table  of  Composition,        .....  40 

Table  for  Determinations,                            .         .  42 

STUDY  IX.     QUARTZOSE  ROCKS,  .  *      .  .44 

STUDY  X.     MICACEOUS,  AMPHIBOLIC,  AND  PYROXENIC  ROCKS,   .         .  50 

I.  Micaceous  Rocks,           .....  50 

II.  Amphibolic,  and  Pyroxenic  Rocks,        .         .  52 

STUDY  XL     FELSITIC,  HYDROUS  MAGNESIAN,  AND  ALUMINOUS  ROCKS,  56 

I.  Felsitic  Rocks,     .  56 

II.  Hydrous  Magnesian  Rocks,           ...  58 

III.  Aluminous  Rocks, 60 

ix 


X  CONTENTS. 

STUDY  XII.     CALCAREOUS  ROCKS, 61 

STUDY  XIII.     CARBONACEOUS.  IRON  ORE,  AND  ERUPTIVE  ROCKS,      .       67 

I.  Carbonaceous  Rocks,      .....       67 

II.  Iron  Ore  Rocks,  .  ...       69 

III.  Eruptive  Rocks, 70 

STUDY  XIY.     RETROSPECT  OF  THE  ROCKS, 72 

Table  of  Rock  Structure,   .....  74 

Table  of  Rock  Composition,        ....  75 

Table  for  Rock  Determination,  ....  76 

STUDY  XY.     SEDIMENTATION,  .......       80 

STUDY  XVI.     EROSIONS, 87 

STUDY  XVII.  STRATA,  AND  WHAT  THEY  TEACH,  .  .  .  .97 
STUDY  XVIII.  FOSSILS,  AND  WHAT  THEY  TEACH,  .  .  .102 
STUDY  XIX.  How  THE  STRATA  ARE  DISPOSED,  .  .  .  .108 
STUDY  XX.  GEOLOGICAL  MAPS,  .  .  .  .116 

STUDY  XXI.     GEOLOGICAL  SECTIONS, 123 

STUDY  XXII.     THERMAL  WATERS, 129 

STUDY  XXIII.     VOLCANOES,  .         .         .         .         .         .         .         .138 

STUDY  XXIV.     ANCIENT  LAVAS, 150 

STUDY  XXV.     MOUNTAIN  PHENOMENA, 160 

STUDY  XXVI.     MOUNTAIN  FORMATION,  .  ....     169 

STUDY  XXVII.    VEINS  AND  ORES, 177 

STUDY  XXVIII.     GEOLOGY  OF  SALT,      .  ....     186 

STUDY  XXIX.     GEOLOGY  OF  PETROLEUM, 194 

STUDY  XXX.  EXAMINATION  OF  SOME  CUP  CORALS,  .  .  .202 
STUDY  XXXI.  FURTHER  EXAMINATION  OF  CUP  CORALS,  .  .  210 
STUDY  XXXII.  EXAMINATION  OF  SOME  TABULATE  CORALS,  .  .218 
STUDY  XXXIII.  EXAMINATION  OF  SOME  BRACHIOPODS,  .  .  226 

STUDY  XXXIV.     FURTHER  EXAMINATION  OF  BRACHIOPODS,     .  234 


CONTENTS.  xi 


PART   II.  —  SYSTEM ATIC    STUDIES; 

OR,  OUTLINES  OF  A  LOGICAL    ARRANGEMENT    OF   THE    FACTS, 
WITH  THE  LESSONS  THEY  TEACH. 

GENERAL  DEFINITIONS  AND  DIVISIONS  OF  THE  SUBJECT,      .         .         .  245 

CHAPTER  I.  —  LITHOLOGICAL  GEOLOGY  (Petrography},      .         .         .  248 

§  1.    Chemistry, 248 

§  2.    Mineralogy, 248 

§3.   Kinds  of  Rocks, .         .         .248 

1.  Physical  Conditions  of  Rocks, 248 

(1)  Mineral  Constitution.      («)   Essential   Constitu- 

ents,    (b)  Accessory  Constituents,        .         .     248 

(2)  Physical  Constitution,    (a)  Fragmental.    (b)  Crys- 

talline,   (c)  Relations  of  Rocks  to  Mechanical 
and  Chemical  Actions,          ....     250 

(3)  Stratified  and  Unstratified  States,        .         .         .252 

2.  Methods  of  Studying  Rocks,         ...  .253 

3.  Most  Important  Species  of  Rocks,         ....     254 

CHAPTER  IT.  —STRUCTURAL  GEOLOGY  (Geognosy],          .         .         .255 

§  1.    General  Definitions,     ....  ...     255 

§  2.   Accidents  of  Stratified  Rocks, 256 

1.  Accidents  of  Sedimentation,         .....     256 

2.  Accidents  of  Secondary  Origin,    .....     257 

3.  Attitudes  of  Strata .260 

4.  Erosion  of  Strata,        .  .     263 
§3.    Conditions  of  Unstratified  Rocks,          .  .264 

1.  The  Erupted  Condition,  .  .     264 

2.  The  Intrusive  Condition,  .  .         .         .         .         .265 

3.  The  Vein  Condition,    .  .  .265 
§  4.    Classification  of  Formations,  .  .     265 

1.    Evidences  of  Relative  Age,  .  .  265 

(1)  From  Superposition,      .               .         .          .  .  265 

(2)  Evidence  from  Fossils,        .  .  266 

(3)  Evidence  from  Intersections  of  Vein  Matter,  .  267 

(4)  Method  of  Combining  the  Observations,       .  .  267 


xii  CONTENTS. 

2.  The  Cycle  of  Sedimentation, 268 

3.  General  Terms  Employed  in  Classification,  .         .         .  269 

4.  Table  of  Geological  Equivalents,          ....  273 

CHAPTER  III.  —  DYNAMICAL  GEOLOGY, 276 

§  1.   Agency  of  Water, 276 

1.  Running  Water,          ...                   ...  276 

2.  Oceanic  Action, 279 

(1)  Ocean  Currents,          .         .  •       .         .         .         .279 

(2)  Wave  Action,    ...                  ...  279 

3.  Action  of  Ice,     ....  .  .280 

4.  Assortment  of  Marine  Sediments,         ....  283 

§  2.    Agency  of  the  Atmosphere,          ......  284 

1.  Wear  by  Wind-borne  Sands, 284 

2.  Sand  Dunes,        ...                   ....  285 

3.  Transportation  of  Volcanic  Ashes,        ....  286 

§  3.   Agency  of  Heat, 286 

1.  Geological  Results  of  Former  High  Temperature,         .  287 

(1)  A  Primitive  Molten  State,  .         .         .         .287 

(2)  Origin  of  Erupted  Materials,       ....  289 

(3)  Agency  of  Steam  in  Eruptive  Action,          .         .  289 

(4)  Metamorphism— Filling  of  Veins,       .         .         .289 

2.  Effects  of  the  Earth's  Cooling, 291 

(1)  Contraction  and  Lateral  Pressure,       .         .         .  291 

(2)  Evolution  of  Heat, 292 

(3)  Seismic  Results  of  Contraction,            .         .         .  292 

(4)  Mountain  Making 293 

§  5.    Geological  Climates,              295 

1.  Terrestrial  Causes, 295 

(1)  Greater  Heat  and  Greater  Uniformity  of  Primi- 

tive Climates, 295 

(2)  Alleged   Antecedent    Habitability    of    Northern 

Regions,          .......  295 

(3)  Ultimate  Total  Dissipation  of  Terrestrial  Heat,   .  296 

(4)  Ultimate  Extinction  of  the  Sun,          .         .         .  296 

2.  Extra-Terrestrial  Causes  of  Climate,    .                            .  297 

§  6.    Tidal  Action  in  the  Earth's  History,     .         .         .         .         .297 

1.  Definitions, 297 

2.  Seismic  Consequences  of  Tidal  Action,          .         .  298 

3.  Tidal  Evolution  of  Heat, 298 

4.  Tidal  Influence  on  Motions  of  Earth  and  Moon,    .         .  299 


CONTENTS.  Xlii 

(1)  Lagging  of  the  Tide, 299 

(2)  Retardation  of  the  Earth's  Rotation,  .         .     299 

(3)  Diminution  of  Earth's  Oblateness,       .         .         .     299 

(4)  Increase  of  the  Moon's  Distance,         .         _         .300 

5.  High  Primitive  Marine  Tides  and  the  Consequences,     .     300 

6.  Ingrained  Meridional  Trends  in  the  Perth's  Crust,        .     301 

§  7.    Geotechtonic  and  Scenographic  Results,        ....     302 

CHAPTER  IV.     PROGRESS  OF  TERRESTRIAL  LIFE,   .         .         .         .303 

Definitions — Fossilization — Horizontal    Range — Vertical    Range — 

Colonies,      ....  .     303 

§  1.    Most  Important  Types  of  Plants  and  Animals,      .         .         .305 

1.  Plants — General  Classification,    .         .         .         ."   »    .     305 

2.  Animals — General  Classification,          ....     306 

Stem  I.  Protozoa.  Stem  II.  Ccelenterata.  Stem 
III.  Echinodermata.  Stem  IV.  Vermes.  Stem  V. 
Mollusca.  Stem  VI.  Arthropoda.  Stem  VII.  Ver- 
tebrata. 

§  2.    Nature  of  the  Succession  of  Organic  Forms,  .     314 

1.  The   Succession   a   General   Progress    from    Lower   to 

Higher,  .  .315 

2.  Earlier  Animals  Generally  Comprehensive,  .     316 

3.  The  Graduation  Not  Complete,    .  .317 

§  3.  The  Dawn  Animal,      ....  .318 

§4.  Trilobites, -323 

§5.  Crinoids, .         .     324 

§  6.  Chambered  Shells, -326 

§7.  Fishes, -331 

§  8.  Reptiles,     ....  .335 

§  9.  Toothed  Birds,    ...  .343 

§  10.    Mammals,          ....  .         .     345 

1.  Mesozoic  Mammals,    . 

2.  Tertiary  Mammals,     . 

§  11.    Retrospect  of  Succession  of  Vertebrate  Life  in  America,  357 

§  12.    Conspectus  of  Geological  Range  and  Relative  Expansion  of 

Principal  Types  of  Animal  Life,      .  •     359 


xiv  CONTENTS. 

CHAPTER  V.     FORMATIONAL  GEOLOGY, 360 

§  1.    Preliminaries.     Geological  Maps, 360 

§  2.    The  Eozoic  Great  System, 361 

1.  How  the  Term  is  Used, 361 

2.  Divisions  of  the  Great  System, 362 

3.  Geographical  Distribution  and  Surface  Exposures,         .  363 

4.  General  Constitution  of  the  Great  System,  .         .  364 

5.  Kinds  of -Rocks  and  Economic  Products,      .         .         .  365 

6.  Organic  Remains, 368 

§  3.   The  Cambrian  System,         ....  .  369 

1.  Divisions,  Subdivisions  and  Terms,       ....  369 

2.  Geographical  Extension, 370 

3.  The  Continent  at  the  Beginning  of  the  Cambrian  Age,  371 

4.  Cambrian  Rocks  and  Minerals, 373 

5.  Erosion  Features, 376 

6.  Organic  Remains, 379 

§  4.   The  Silurian  System, 381 

1.  Divisions,  Subdivisions,  and  Terms,     ....  381 

2.  Geographical  Extension, 381 

3.  The  Continent  at  the  Beginning  of  Silurian  Time,        .  382 

4.  Silurian  Rocks  and  Minerals,        .         .  .  384 

5.  Erosion  Features,        ....  .  386 

6.  Organic  Remains, 387 

§  5.    The  Devonian  System,          ...  .  389 

1.  Divisions,  Subdivisions,  and  Terms,  ...  .  389 

2.  Distribution  and  Lithological  Features,        .         .         .  390 

3.  Erosion  Features, .  392 

4.  Organic  Remains,        .  ....  394 

§  6.    The  Lower  Carboniferous  System, 395 

1.  Divisions,  Subdivisions,  and  Terms,     ....  395 

2.  Distribution  and  Lithological  Features,         .         .         .  396 

3.  Geography  of  the  Continent  during  the  Lower  Carbon- 

iferous Age,     ........  399 

4.  Erosion  Features,        ....  .  401 

5.  Organic  Remains,        .......  401 

§  7.    The  Upper  Carboniferous  System, 402 

1.    Divisions,   Subdivisions,    and  Terms.     Table    of    Coal 

Measures, .402 

Standard  Section  of  the  Coal  Measures,     .         .         .  403 


CONTENTS.  XV 

2.  Distribution,       ........  406 

3.  Kinds  of  Rocks, 407 

4.  Geological  Structure, 410 

5.  Coal  Mining, 413 

6.  Organic  Remains,        .......  416 

7.  Origin  of  Mineral  Coal, 421 

8.  Growth  of  the  Land  during  the  Upper  Carboniferous,  422 

§  8.    The  Mesozoic  Great  System, 424 

1.  Divisions,  Subdivisions,  arid  Terms,     .         .         .         .  424 

2.  The  Triassic  System,  .         .         .         .         .         .424 

3.  The  Jurassic  System, 427 

4.  The  Cretaceous  System,        ......  429 

(1)  Distribution  and  Kinds  of  Rocks,        .         .         .  429 

(2)  Economic  Products  of  the  Cretaceous,         .         .  431 

(3)  Fossil  Remains  of  the  Cretaceous,        .         .         .433 

5.  The  Physiognomy  of  the  Interior  of  the  Continent,       .  434 

6.  Comparative  Geology  of  the  Provinces,         .         ...  436 

7.  Geological  History  of  the  Cordilleran  Region,       .         .  437 

§  9.   The  Ca3nozoic  Great  System,         .         .         .         .  %     .         .  441 

1.  Divisions,  Subdivisions,  and  Terms,     ....  441 

2.  Geographical  Distribution  of  the  Tertiary,   .         .         .  442 

3.  Organic  Remains  of  the  Tertiary,         ....  444 

4.  Quaternary  Materials,           .         .         ...         .         .  444 

(1)  Phenomena  of  the  Surface  Materials,           .         .  445 

(2)  Relation  of  Drift  Phenomena  to  Climatic  Causes,  446 

(3)  More  Critical  Observation  of  the  Drift,       .         .  447 

(4)  The  Terminal  Moraine  of  the  Ancient  Glacier,   .  448 

(5)  Characteristics  of  the  Terminal  Moraine,              .  450 

(6)  Tabular  Limestone  Masses  Imbedded  in  the  Drift,  451 

(7)  Champlain  Deposits,            .                                     .  452 

(8)  Quaternary  Lakes 452 

(9)  Recent  Formations, 454 

(10)  Organic  Remains  of  the  Quaternary,                   .  456 

CHAPTER  VI.  — HISTORICAL  GEOLOGY, 463 

§  1.    Presedimentary  History,       ...                            .  463 

§  2.    Inductive  History,       .         .         .  . 465 

1.  The  Eozoic  ^on,         .                                     ...  465 

2.  The  Palaeozoic  JEon,    .                                                        .  468 

(1)  Movements  of  the  Lands,  .                  .         .         .  468 

(2)  Progress  of  Animal  Organization,        .         .         .  469 


XVI  CONTENTS. 

(3)  The  Coal  Period, 470 

(4)  Close  of  the  Paleozoic, 471 

3.  The  Mesozoic  ^Eon, 472 

(1)  Continental  History, 472 

(2)  Progress  of  Mesozoic  Life,          ....  475 

4.  The  Caenozoic  ^Eon, 476 

(1)  The  Tertiary  Age, 476 

(2)  The  Glacial  Epoch,              479 

(3)  The  Champlain  Epoch 483 

(4)  Effects  of  Glacier  Pressure,         .  .485 

(5)  The  Recent  Epoch, 486 

§3.    Ulterior  History, 488 


LIST  OF  TABLES. 


COMPOSITION  OF  THE  FELDSPARS, 28 

STANDARDS  OF  HARDNESS, 42 

COMPOSITION  OF  THE  COMMON  MINERALS, 40,  41 

FOR  DETERMINATION  OF  MINERALS,     ......  42-11 

ROCK  STRUCTURES, '  74 

ROCK  COMPOSITION, 75 

FOR  ROCK  DETERMINATION, 76-80 

TYPES  OF  MOUNTAIN  STRUCTURE, 167 

CONSPECTUS  OF  THE  GEOLOGY  OF  PETROLEUM,      ....  199 

STRUCTURES  OF  BRACHIOPODS, 240 

ANALYTICAL  TABLE  FOR  IDENTIFICATIONS, 240 

CYCLES  OF  SEDIMENTATION, 268 

TABLE  OF  GEOLOGICAL  EQUIVALENTS, 274,  275 

MOST  IMPORTANT  TYPES  OF  PLANTS  AND  ANIMALS,       .         .        .  305-314 

FORMS  OF  CHAMBERED  SHELLS,   .                          ....  329 

SUCCESSION  OF  VERTEBRATES  OF  NORTH  AMERICA,        .         .         .  358 

RANGE  AND  EXPANSION  OF  ORGANIC  TYPES,         ....  359 

STANDARD  SECTION  OF  COAL  MEASURES, 403-405 


XVll 


LIST  OF  MAPS. 


WINDINGS  OF  THE  MISSISSIPPI, 84 

GEOLOGICAL  MAP  OF  THE  UNITED  STATES  (2  pages),     .         .         .     118,  119 

MAP   OF   ^TNA    AND   ITS    ERUPTIONS,      .             .             .             .             .             .  141 

MAP  OF  HAWAII,  SHOWING  LAVA  FLOWS,    .         .         .                 .  144 

GEOLOGICAL  MAP  OF  NORTH  AMERICA,          .         .         .         .         .  361 

COAL  MAP  OF  PENNSYLVANIA  AND  OHIO, 407 

MAP  OF  TERMINAL  MORAINE  IN  THE  UNITED  STATES,  .         .         .  449 

SUBMARINE  CHANNEL  OF  THE  HUDSON  RIVER,      ....  455 

^EONIC  MAPS. 

NORTH  AMERICA  NEAR  THE  CLOSE  OF  THE  Eozoic  ^EoN,       .         .  371 

NORTH  AMERICA  NEAR  THE  BEGINNING  OF  THE  SILURIAN  AGE,      .  383 
NORTH  AMERICA  NEAR  THE  BEGINNING  OF  THE  CARBONIFEROUS  AGE,        399 

NORTH  AMERICA  NEAR  THE  BEGINNING  OF  THE  COAL  PERIOD,       .  423 

NORTH  AMERICA  NEAR  THE  BEGINNING  OF  THE  MESOZOIC  JEox,    .  439 

NORTH  AMERICA  NEAR  THE  BEGINNING  OF  THE  CRETACEOUS   AGE,  440 

NORTH  AMERICA  NEAR  THE  BEGINNING  OF  THE  C^ENOZOIC  ^ON,   .  477 

xviii 


SUGGESTIONS  TO  THE  INSTRUCTOR. 


1.  Adhere  scrupulously  to  the  method  of  the  book.     Vary  the  facts, 
illustrations,  comments,  and  inferences  according  to  opportunity  or  ability. 

2.  Do  not  permit  any  persons  to  thrust  upon  your  attention,  or  that  of 
the  pupils,  any  specimens  not  yet  considered  in  the  book.     Most  persons 
have  a  few  treasured  minerals  from  some  remote  mining  region  upon  which 
you  will  be  asked  to  pronounce  opinions.    Do  not  be  annoyed  by  them.    The 
specimens  at  your  door  are  incalculably  more  important. 

3.  Give  deliberate  attention  to  the  exercises.    See  that  every  pupil  learns 
to  elucidate  every  subject  presented  in  them.     Occasionally  a  question   is 
raised  which  even  the   teacher  may  not  be   prepared  to  solve.     That  is 
intended.     It  is  profitable  to  have  something  to  study  over. 

4.  If  the  class  is  small —  say,  not  over  a  dozen  —  they  may  be  ordinarily 
taken  into  the  field.     This  is  always  the  best  course.     If  the  class  is  large, 
the  subject  may  be  pursued  chiefly  in   the   class-room ;  but   illustrations 
should  be  abundant.     In  the  study  of  minerals  and  rocks,  a  large  supply  of 
specimens,  all  broken  from  the  same  bowlder,  may  be  furnished,  and  one 
specimen  placed  in  the  hands  of  each  student.     The  teacher  will  then  direct 
attention  to  every  character  visible  in  the   specimen,   pursuing  the  same 
method  as  the  teacher  of  botany.     The  rock  must  have  been  previously 
selected  with  reference  to" showing  what  is  treated  in  the  study  appointed  for 
the  day. 

When  this  specimen  is  well  understood,  another  set  may  be  distributed, 
and  so  on. 

5.  After  a  few  exercises  of  this  kind,  individual  students  may  be  re- 
quired to  name  such  minerals  in  the  specimen  in  hand  as  have  been  pre- 
viously studied.     Then,  after  the  work  is  more  advanced,  a  mixed  lot  of 
specimens  may  be  brought  in,  and  individual  students  requested  to  deter- 
mine them.     Eeports  should  be  made  on  slips  of  paper,  and  returned  with 
the  specimen.     These  may  be  examined  immediately,  if  time  permits,  or 
after  the  exercise.     The  student's  report  should  state  all  the  facts  on  which 
the  name  of  the  specimen  depends :  Stratified  or  not ;  thick-  or  thin-bedded ; 
what  essential  minerals;  what  accessory  minerals;  the  name.     These  exer- 
cises should  be  continued  for  many  days  after  the  end  of  the  subject  of  rocks 
is  reached  in  the  book. 

xix 


XX  SUGGESTIONS   TO   THE   INSTRUCTOR. 

6.  Get  supplies  of  rock  specimens,  if  the  class  is  large,  by  having  two 
students  volunteer  to  bring  a  basket  full  on  the  following  day,  and  two  others 
to  bring  another  basket  full,  and  so  on.     The  specimens  should  be  preserved 
in  drawers  for  future  use,  both  during  the  present  and  subsequent  terms.    If 
the  class  is  small,  a  supply  should  be  in  store  for  use  when  the  weather  may 
prevent  field  work. 

7.  Generally,  fragments  of  bowlders  broken  for  building  purposes  may 
be  found,  and  further  reduced  with  the  small  hammers.    If  not,  the  collector 
must  use  a  large  hammer  for  breaking  bowlders.     This  should  belong  to  the 
school.     If  necessary,  a  workman  may  be  taken  along.     In  some  cases  it  will 
be  most  convenient  to  have  a  large  supply  of  bowlders  brought  into  one 
corner  of  the  yard,  or  deposited  under  a  shed.     These  may  all  be  coarsely 
broken  at  once  by  a  workman.     Smaller  fragments  may  be  produced  by  the 
students  as  needed ;  but  specimens  from  the  same  bowlder  should  be  kept 
together.     This  method  may  be  best  suited  to  some  girls'  schools,  to  institu- 
tions in  large  cities  and  in  other  localities  where  Drift  specimens  are  not 
easily  accessible. 

In  a  region  destitute  of  bowlders  a  supply  may  be  obtained  from  seme 
bowlder-covered  region,  by  causing  to  be  shipped  as  freight  a  number  of 
bowlders  of  different  sorts  of  rocks,  either  unbroken  and  unboxed  or  broken 
into  hand  specimens  and  boxed.  The  author  has  already  sent  boxed  speci- 
mens to  the  southern  states  and  to  the  Illinois  prairies. 

9.  Encourage  the  procurement  of  a  good  supply  of  hammers  and  lenses 
by  the  students.     They  may  be  regarded  as  essential  to  satisfactory  work. 
The  lenses  are  almost  indispensable  in  the  examination  of  rocks. 

10.  Encourage  the  formation  of  private  collections,  and  see  that  they  are 
kept  properly  ticketed.     See  that  a  good  collection  is  formed  for  the  school. 
Procure,  if  possible,  from  some  dealer  a  standard  collection  of   common 
minerals  and  rocks. 

11.  Embrace  every  opportunity  to  require  drawings.     Blackboard  draw- 
ings are  useful ;  but  careful  sketches  on  drawing  paper  are  better.     Sketches 
of  cliffs,  quarries,  gravel  banks,  ravines,  fossils,  or  any  other  geological  fea- 
tures or  phenomena  should  be  required  of  all. 

12.  Dwell  long  on  the  subject  of  geological  sections.     Nothing  is  a  more 
useful  exercise  for  the  pupil  than  the  construction  of  sections  from  the  geo- 
logical map.     If  the  locality  permits,  have  the  students  also  construct  sec- 
tions, with  measurements,  from  the  field. 

13.  Require  each  student  to  construct  a  tinted  geological  map.     Prefer- 
ably a  map  of  the  United  States  east  of  the  Black  Hills,  or  better,  of  the 
whole  country.     The  maps  in  the  text  book  may  be  enlarged ;  or,  for  more 
accuracy,  the  map  of  the  U.  S.  Geological  Survey  may  be  used. 

14.  Require  every  student  to  make,  also,  collections  of  fossils,  and  to 


SOME   PRACTICAL   HINTS.  xxi 

determine  their  names  if  possible.  Do  not  fail  to  secure  exercises  in  grind- 
ing, polishing,  and  investigating,  as  indicated  in  Study  XXX  of  this  book. 
15.  The  production  of  a  neat  and  accurate  geological  map  may  well 
abate  considerably  the  rigor  of  a  final  examination.  The  same  may  be  said 
of  a  well  labelled  collection  of  specimens,  or  a  number  of  well  prepared  thin 
sections,  or  a  larger  number  o£  polished  surfaces  of  rocks  or  fossils.  In  this 
first  stage  of  the  study,  the  senses  and  the  hands  are  to  be  kept  in  full  exer- 
cise. These  will  supply  motives  for  the  pleased  activity  of  imagination, 
memory,  and  the  reasoning  powers. 


SOME  PRACTICAL  HINTS. 

Hammers. — The  best  forms  of  Hammers  for  general  use  are  shown  in 
Figs.  1  and  2.  The  palaeontologist's  pattern,  with  pene  a  tapering  and 
sharp,  and  transverse  to  the  handle,  is  by  far  most  convenient  in  collecting 
fossils.  The  face  b  should  be  flat,  square  cornered,  and  longest  in  the  direc- 


b 

FIG.  1.— GEOLOGICAL  HAMMER.    PALJJC-  FIG.  2.— GEOLOGICAL  HAMMER.    QUARRY- 

ONTOLOGIST'S  PATTERN.  MAN'S,  OR  STONEMASON'S,  PATTERN. 

tion  of  the  handle.  The  eye  should  be  large ;  the  handle  of  hickory,  thick, 
short,  and  shaped  as  shown,  and  fastened  in  with  two  iron  wedges.  Weight 
may  be  from  half  a  pound  to  a  pound.  For  working  among  very  hard  rocks, 
the  stonemason's  pattern  is  better.  The  pene  is  parallel  to  the  handle,  less 
tapering,  and  blunter.  The  temper  of  all  hammers  should  be  that  required 
by  the  stonemason.  Notice,  the  pene  of  the  palaeontologist's  hammer  must 
not  be  used  on  quartzose  rocks. 

Larger  quarryman's  hammers,  with  long  handles  for  use  with  both 
hands,  and  weighing  from  two  to  five  pounds,  are  needed  for  breaking  large 
bowlders ;  but  one  at  the  service  of  the  class  is  sufficient. 

Using1  the  Hammer. — A  blow  with  the  flat  face  of  the  hammer  in  the 
middle  of  a  fragment  shatters  it  irregularly.  A  blow  with  the  face  a  little 
inclined,  or  with  the  pene  of  the  hammer,  tends  to  produce  a  fracture  in  the 
direction  of  the  face-edge,  or  the  pene.  If  the  object  is  to  reduce  the  size  of 


XX11 


SOME   PRACTICAL   HINTS. 


a  specimen,  or  dress  it  into  form,  a  quick,  sharp  blow  with  the  face-edge  or 
the  pene,  delivered  near  the  margin  of  the  specimen,  will  cause  a  break  only 
along  the  line  of  contact.  If  the  edge  is  too  thick  to  break  in  this  way, 
make  it  thinner  by  clipping  off  with  blows  along  the  edge  near  the  angles. 

A  steel-faced  anvil,  weighing  ten  to  twenty  pounds,  is  useful  in  dressing 
specimens,  and  in  breaking  up  masses  for  the  removal  of  fossils.  For  the 
former  object,  hold  the  specimen  so  that  the  portion  to  be  removed  projects 
beyond  the  anvil  face,  and  the  specimen  rests  solidly  on  the  edge  of  the  face. 
Then  strike  a  sharp  blow  on  the  projecting  part,  and  it  will  break  off  along 
the  line  of  contact  with  the  anvil. 

To  break  a  large  bowlder,  strike  repeatedly -with  the  pene  of  a  heavy 
quarry  man's  hammer  along  a  selected  line.  Sooner  or  later  the  bowlder  will 
split. 

Hardness  Tester. — A  steel  rod,  wedge-shaped  and  pointed  atone  end, 


FIG.  3.— HARDNESS  TESTER,    a,  View  of  the  Flattened  Side  of  Point.    6,  View  of  the 
Taper  toward  the  Point. 

as  shown  in  Fig.  3,  is  convenient ;  but  an  old  three-cornered  file  ground  to 
a  point  is  just  as  efficient.  In  default  of  both,  a  well  tempered  knife  point 
may  be  used.  Whatever  tester  is  adopted,  use  the  same  habitually. 

Magnifiers. — A  simple  pocket  magnifier  is  indispensable  in  the  exam- 
ination of  minerals  and  rocks.  A  glass  with  a  single 
lens  will  be  suitable.  A  larger  size  than  these  figured 
is  preferable.  Get  nothing  but  a  pocket  magnifier. 

Acid. — A  small  glass-stoppered  bottle  of  dilute 
chlorhydric  (muriatic)  acid  should  be  at  hand  in  the 
class  room  for  testing  carbonates.  A  drop  may  be 
taken  out  on  the  tip  of  a  blunt  stick,  and  applied  to 
the  specimen.  In  the  lack  of  such  acid  very  strong 
vinegar  will  answer  in  some  cases;  but  do  not  depend 
on  it. 

Tickets. — Small  tickets,  to  be  permanently  at- 
tached to  specimens  to  receive  numbers,  may  be  cir- 
cular, oval,  or  other  shape,  three-sixteenths  of  an 
inch  (five  millimetres)  in  diameter,  punched  from  thin  white  or  colored 
paper  that  will  take  ink.  A  common  saddler's  or  tinner's  punch  may  be 
used.  Fold  the  paper,  and  punch  through  many  thicknesses  with  one  blow, 


FIG.  4. — MAGNIFIERS. 
a,  Oval.  6,  Bellows 
Shaped. 


SOME   PRACTICAL   HINTS.  xxiii 

resting  on  a  block  of  lead  or  wood.     As  the  tickets  will  tend  to  adhere,  lay  a 
quantity  in  the  palm  of  one  hand,  and  rub  them  with  the  finger  tips  of  the 
other.     Square,  oblong  or  triangular  tickets  may  be  cut  with  scissors. 
Cement. — Do  not  use  common  mucilage.     Take 

Clear  Gum  Arabic        .....        2  ozs. 

Fine  Starch \%  oz< 

White  Sugar %  oz> 

Pulverize  the  gum  arabic  in  a  mortar,  and  dissolve  in  so  much  water  as  the 
laundress  would  use  for  the  quantity  of  starch  indicated.  Dissolve  the 
starch  and  sugar  in  the  gum  solution.  Then  cook  the  mixture  in  a  vessel 
suspended  laundry  fashion,  in  boiling  water,  until  the  starch  becomes  clear. 
The  cement  must  be  as  thick  as  tar,  and  must  be  kept  so.  Use  from  a  wide- 
mouthed  bottle,  having  a  small  round  bristle-brush  passing  through  the 
cork.  Keep  from  spoiling  by  means  of  a  lump  of  camphor  gum,  or  a  little 
oil  of  cloves  or  sassafras.  Do  not  use  cement  that  has  grown  sour  and  thin. 
Some  of  the  fresh-made  cement  may  be  hard-dried  in  greased  patty-pans, 
and  then  removed  and  kept  indefinitely,  to  be  softened  when  needed  —  a 
good  expedient  for  a  long  journey.  This  cement  may  be  used  to  repair  min- 
erals, rocks,  or  fossils,  and  to  attach  tickets.  One  lot  of  cement  will  serve 
several  persons. 

Attaching  Tickets.— Spread  a  quantity  of  specimens  on  a  table,  with 
the  side  to  be  ticketed  turned  up.  Spread,  also,  a  quantity  of  tickets,  so 
separated  as  to  lie  singly.  With  the  point  of  the  brush,  touch  half  a  dozen 
specimens  in  the  proper  place  with  the  cement.  With  the  moistened  tip  of 
the  finger,  lift  a  ticket,  and  press  it  on  a  gummed  spot.  Press  firmly,  till 
the  ticket  takes  the  shape  of  the  surface,  and  the  cement  is  forced  quite  to 
the  edges.  Then,  as  some  cement  adheres  to  the  finger,  rub  the  finger  tip 
on  a  damp  towel.  This  removes  the  cement,  and  leaves  the  finger  damp  to 
lift  another  ticket.  Thus  the  process  of  attaching  is  expeditious. 

The  Numbers. — To  write  the  numbers  on  the  tickets,  after  well  dried, 
use  perfectly  black  ink,  and  a  sharp,  good,  and  fresh  steel  pen.  Make  your 
very  plainest  figures.  These  are  a  permanent  record ;  illegible  numbers  are 
a  vexation.  The  numbers  refer  to  a  register,  where,  against  corresponding 
numbers,  may  be  found  columns  giving  name,  locality,  how  obtained,  and 
other  information.  Separate  labels  bearing  the  names  and  the  same  num- 
bers may  also  be  used. 

Colored  Tickets. — If  each  person  in  a  class  or  company  adopts  a  par- 
ticular color  for  his  tickets,  then  all  the  specimens  of  the  company  may  be 
mixed,  and  may  be  classified  as  one  lot;  and  afterward  each  person  can 
select  his  own.  See  that  the  colored  paper  is  writing  paper,  and  color  dis- 


XXIV 


SOME   PRACTICAL   HINTS. 


tinct  and  fast.  Separate  ownership  may  also  be  indicated  by  the  form  of 
the  ticket. 

Map  Drawing. — To  put  the  preliminary  geography  on  the  sheet  is 
a  valuable  exercise,  but  is  not  a  study  of  geology.  The  work  may  be  done 
as  an  accessory  in  the  study  of  geography,  or  an  exercise  in  drawing.  For 
our  purpose  procure  blank  (uncolored)  printed  maps  if  possible.  These  may 
sometimes  be  had  of  map  publishers.  Rand,  McXally  &  Co.,  of  Chicago, 
have  for  some  years  supplied  the  University  of  Michigan.  They  print  a  very 
large  assortment  of  maps ;  but  they  do  not  keep  in  stock  blank  impressions 
such  as  we  need;  they  have  to  be  specially  printed  when  called  for,  and  the 
call  should  be  for  fifty  or  more.  The  writer  uses  a  map  of  the  entire  United 
States;  and  the  best  suited  is  their  so-called  "standard  map,"  twenty-six 
inches  by  forty-three  and  one-half  inches,  1882 ;  or  the  later  one,  thirty  and 
one-half  inches  by  forty  inches,  1885.  Either  is  a  complete  railroad  map. 
When  geologically  colored  and  mounted,  it  makes  a  useful  chart  for  reference, 
as  well  as  a  pleasing  souvenir  of  faithful  work. 

Cloth  Backing. — This  is  not  essential  but  very  serviceable.  Dampen 
a  piece  of  fine  muslin  of  requisite  size.  Stretch  it  firmly  on  a  smooth  board 
by  tacking  it  down.  Paste  the  back  of  the  map  with  smooth  flour  paste  applied 
with  a  large,  stiff,  flat  brush.  Lay  the  pasted  surface  on  the  stretched  cloth, 
carefully  excluding  all  air  by  holding  the  edges  of  the  map  up  and  allowing 
the  centre  to  come  first  in  contact.  Press  the  two  surfaces  together  by  rub- 
bing from  the  centre  toward  the  sides  through  the  medium  of  a  cloth.  It  is  best 
to  leave  the  whole  attached  to  the  board  or  table  until  the  map  is  completed. 
Then  the  edges  may  be  trimmed,  and  the  map  mounted  on  rollers. 

Geological  Colors. — As  yet,  no  set  of  colors  has  been  agreed  upon  for 
general  use ;  but  the  following  table  indicates  customary  usage : 


FORMATIONS. 

Tertiary. 

Cretaceous. 

Jura-Trias. 

Upper  Carboniferous. 

Lower  Carboniferous. 

Devonian. 

Silurian. 

Cambrian. 

Eozoic. 

Eruptive. 


COLORS. 
Yellow. 
Green. 
Purple. 
Brown. 
Blue. 

Yellowish  Brown. 
Red  Purple. 
Slate. 
Orange  Red. 


MATERIALS. 

Gamboge. 

Gamboge  and  Blue  Ink. 

Carmine  and  Blue  Ink. 

Burnt  Umber. 

Blue  Ink. 

Gamboge  and  Burnt  Umber. 

Blue  Ink  and  Much  Carmine. 

India  Ink  and  Blue  Ink. 

Carmine  Ink  and  Gamboge. 

Carmine  Ink. 


Bright  Red. 

The  above  is  sufficiently  detailed  for  the  elementary  student,  and  requires 
but  a  very  simple  outfit,  one  of  which  will  supply  several  persons.  When 
subdivisions  of  these  formations  are  to  be  indicated,  use  lighter  and  deeper 


SOME    PRACTICAL   HINTS. 


XXV 


shades  of  the  same  colors— the  lighter  for  the  newer  formations.  For 
deeper  yellow,  orange  may  be  used.  Put  on  a  blank  space  a  legend  explan- 
atory of  the  colors. 

These  colors  may  be  used  on  the  map  published  in  the  text  book.  They 
may  also  be  used  on  sections. 

Avoid  colors  too  deep.  Avoid  the  use  of  too  much  paint.  Make  sharp, 
clean  outlines.  Be  exact.  Use  large  camel's  hair  brushes. 

Wall  Maps.— Get  cotton  sheeting  of  requisite  width,  and  cut  length  in 
proportion  to  the  width  —  calculating  from  the  dimensions  of  the  map  to  be 
enlarged.  Use  dry  pulverized  colors  mixed  in  weak  glue  water.  Stretch  the 
cloth  on  a  frame  erected  vertically  in  a  room.  It  may  be  like  a  quilting 
frame,  in  four  pieces,  with  holes  and  pegs  for  varying  the  size.  Tack  the 
cloth  thoroughly.  Prepare  the  ground  with  one  or  two  coats  of  whiting  and 
glue  water.  When  dry,  pencil  in  lines  of  latitude  and  longitude,  at  inter- 
vals calculated  from  the  map  to  be  copied;  and  from  these  pencil  in  the 
geography.  In  the  same  manner  lay  down  the  geological  outlines.  Then 
apply  the  colors,  and  lastly  put  in  the  lettering,  rivers,  boundaries  and  what- 
ever else  requires  the  black — which  will  be  made  of  lampblack  and  glue 
water.  You  cannot  put  the  colors  over  the  lampblack.  Do  not  omit  the 
explanatory  legend.  Cut  the  top  and  bottom  straight  and  mount  on  rollers. 
Caution :  Use  only  glue  enough  to  make  the  colors  adhere. 

INCHES 


1 

I2 

.    3! 

1     1     !     1     1     1 

i  !  i  1  i  1 

i  1  i 

>  1  ,  1  i  1  >  ! 

1   :  i      1 

1,1 

ill 

'3 

4                    5 

Ed 

^H 

MILLIMETRES 


GEOLOGICAL  STUDIES. 


PART  I. 
FIELD   STUDIES; 

OR,    HOW    WE    MAY    OBSERVE    THE    FACTS    AND    LEARN    THEIR 
MEANING. 

STUDY   I.— Surface  Materials. 

I  DESIRE  by  some  natural  and  pleasant  method  to  introduce 
my  young  friends  to  the  science  of  geology.  I  trust  the 
study  of  the  subject  will  prove  entertaining,  but  I  shall  endeavor 
at  the  same  time  to  put  them  on  a  truly  scientific  course.  The 
method  which  seems  most  suitable  for  us  in  the  beginning  is  that 
called  inductive.  We  propose  to  see  things  for  ourselves,  and 
draw  our  own  conclusions  from  them.  For  the  present  we  will 
confine  our  attention  mostly  to  such  things.  But  when  our 
walks  shall  have  extended  over  the  fields  most  accessible  to  us, 
we  will  enlarge  our  information  by  talks  on  other  fields  in  which 
other  persons  have  walked. 

As  geology  is  the  science  which  treats  of  the  earth,  we  have 
not  far  to  go  before  beginning  to  learn.  The  earth  is  under  our 
feet;  let  us  direct  our  attention  to  it  and  see  what  facts  may  be 
observed.  These  will  be  geological  facts.  Every  fact  learned 
by  observing  the  earth  is  part  of  the  science;  and  the  things 
observed  near  home  are  just  as  real  science,  and  just  as  impor- 
tant, as  those  in  distant  lands,  of  which  we  may  read  in  the 
books. 


&    '  '  GEOLOGICAL   STUDIES. 

Now,  first  of  all,  we  see  that  the  surface  of  the  earth  is  cov- 
ered by  a  bed  of  loose  materials  consisting  chiefly  of  sand, 
gravel,  small  stones,  and  clay.  We  will  call  these  materials 
Drift,  for  a  reason  which  will  be  understood  hereafter.  The 
uppermost  layer,  which  is  known  as  soil,  is  generally  of  a  darker 
color  and  evidently  contains  some  other  substance.  We  observe 
the  color  darkest,  and  the  depth  of  the  soil  greatest  in  places 
where  most  vegetable  material  goes  to  decay;  as,  for  instance, 
where  many  leaves  accumulate  from  year  to  year,  or  where 
grasses  or  mosses  have  grown  abundantly  and  decayed,  as  in  low 
meadows  and  swamps.  In  some  situations  the  soil  is  mostly  or 
wholly  composed  of  substances  forming  a  fine  dark  mould,  with 
very  little  gravelly  or  sandy  material  derived  from  the  Drift. 
We  also  observe  that  least  soil  exists  in  situations  where  least 
vegetable  matter  has  decayed,  as  on  dry  knolls  and  along  sterile 
slopes,  where  the  bed  rock  comes  near  the  surface.  It  is  a  fair 
inference  from  these  observations  that  the  matter  which  imparts  a 
darker  color  to  the  upper  layer  of  the  Drift  is  of  a  vegetable 
character. 

Should  it  happen  that  our  observations  begin  in  a  prairie 
region,  like  that  of  central  and  northern  Illinois,  we  should 
notice  a  great  depth  of  dark  soil,  indicating  that  vegetation  must 
have  grown  over  the  surface  with  extraordinary  luxuriance. 
What  we  notice  of  the  native  plants  or  the  growing  crops  quite 
justifies  the  inference.  We  observe,  too,  that  the  land  is  nearly 
level,  and  therefore,  the  matters  resulting  from  vegetable  decay 
have  lain  on  the  spot  where  they  grew,  and  have  not  been  washed 
away  by  flowing  water.  Those  who  dig  wells  on  the  prairies  find 
that  underneath  the  deep  soil  the  material  is  finer  than  the  sub- 
soil of  most  other  regions,  and  has  different  colors.  There  are 
very  few  pebbles  or  cobble  stones  either  in  the  soil  or  the  sub- 
soil. This  prairie  deposit  must,  therefore,  have  been  produced 
in  a  different  way  from  the  common  Drift  of  other  regions. 

But  now  we  visit  some  locality  where  a  deep  excavation  has 
been  sunk,  and  find  that  the  prairie  deposit  does  not  continue 
down  to  the  bed  rock.  At  the  depth  of  thirty,  fifty,  or  a  hundred 


SURFACE    MATERIALS.  3 

feet  we  reach  the  bottom  of  it;  and  then  comes,  generally,  some- 
thing like  the  real  Drift  of  other  regions.  We  examine  it  care- 
fully. There  are  the  same  sand  and  gravel,  the  same  rounded 
stones,  as  make  up  the  Drift  elsewhere.  It  cannot  be  distin- 
guished from  the  Drift.  It  is  the  Drift.  So  we  feel  authorized 
to  draw  another  inference.  The  real  Drift  was  laid  down  over 
much  of  the  prairie  region  the  same  as  over  other  regions. 
Then,  afterward,  by  some  means  the  fine  prairie  deposit  was  laid 
down. 

But  by  far  the  greatest  number  of  us  who  set  out  to  view  the 
surface  of  the  earth  must  walk  over  the  common  Drift.  This  is 
something  so  nearly  alike  from  New  England  to  the  Mississippi 
River,  and  from  Hudson's  Bay  to  the  Ohio,  that  persons  every- 
where will  see  nearly  the  same  things.  So,  wherever,  within  the 
region  indicated,  you  may  begin  this  study,  you  will  be  able  to 
observe  the  geological  facts  which  I  now  intend  to  point  out. 

The  surface  of  the  Drift,  as  you  have  noticed,  is  generally 
rolling.  There  are  hills  and  ridges  and  valleys.  The  streams 
flow  along  the  valleys,  and  they  seem  to  have  been  agencies  in 
the  making  of  the  valleys.  The  forms  of  the  hills  are  rounded, 
and  it  is  easy  to  understand  that  these  have  been  shaped  by  the 
rains.  We  notice,  however,  that  many  of  the  Drift  hills  are 
elongated,  more  or  less,  and  it  is  a  curious  fact  that  in  any  par- 
ticular region  their  longer  diameters  are  all  turned  in  the  same 
direction.  There  must  be  some  explanation  of  this,  and  we  shall 
try  and  discover  it. 


FIG.  5.— DKIFT  HILLS  IN  WISCONSIN.    (Chamberlin.)    See,  also,  Fig.  357. 

When  we  examine  the  materials  of  the  Drift,  we  notice  that 
it  is  composed  mostly  of  sand,  fine  and  coarse,  with  occasional 


4  GEOLOGICAL   STUDIES. 

beds  of  clay.  There  are  many  stones,  large  and  small,  and  they 
are  all  rounded.  We  shall  call  them  all  bowlders.  When  they 
are  not  over  six  or  eight  inches  in  diameter  they  are  known  as 
cobble  stones,  and  are  used  for  rough  paving.  When  they  are  an 
inch  or  less  in  diameter,  down  to  the  size  of  gravel,  we  call  them 
pebbles.  They  are  used  with  gravel  and  sand  in  road  making, 
and  also,  mixed  with  asphaltum  or  coal  tar,  in  sidewalks.  Bowl- 
ders of  all  sizes  are  generally  dispersed  through  the  Drift;  but 
the  larger  bowlders  are  by  no  means  uniformly  dispersed.  Many 
extensive  fields  are  entirely  free  from  them,  while  in  others  they 
form  a  serious  obstruction  to  cultivation.  Here  is  a  view  of  a 
bowlder-covered  field  near  Gloucester,  Mass.  (Fig.  6.) 


FIG.  6.— A  BOWLDER-COVERED  FIELD  NEAR  SQUAM,  IN  GLOUCESTER,  MASS. 
(After  E.  Hitchcock.) 

In  some  parts  of  the  country  where  the  bed  rock  is  completely 
buried  by  Drift,  large  bowlders  are  broken  up  and  used  for 
building  stones.  They  present  a  substantial  and  pleasing  appear- 
ance. 

The  arrangement  of  the  Drift  materials  will  be  noted.  If  we 
go  to  any  railroad  cut  through  the  Drift,  we  see  beds  of  sand  and 
gravel  laid  down  without  any  general  uniformity.  The  beds  pre- 
sent a  variety  of  inclinations,  and  within  the  limits  of  a  single 
bed  the  thinner  layers,  or  lamince,  are  often  seen  to  pass  obliquely 


SURFACE   MATERIALS. 


6  GEOLOGICAL   STUDIES. 

across.  Fig.  7  presents  a  view  of  a  gravel  bank  cut  through  in 
the  construction  of  a  street.  Underneath  the  soil  and  subsoil, 
a  a  a  a,  we  notice  some  gravelly  beds,  b  b  b,  presenting  a  con- 
fused and  oblique  stratification.  These  are  followed  by  horizon- 
tally stratified  sand,  c  c  c  c,  and  two  courses  of  pebbles,  d  d  d 
and  e  e  e,  separated  by  a  stratum  of  pebbly  sand  which  is  obliquely 
laminated.  Still  lower  is  another  bed  of  gravel,  f  f  f,  distinctly 
laminated,  but  in  the  other  direction.  This  passes,  toward  the 
right,  into  another  bed,  g  g,  with  lamince  inclining  to  the  right. 
At  A  A  is  another  stratum  of  fine  buffish  sand  with  lamination 
inclined  steeply  to  the  right.  At  the  foot  of  the  bank  is  a 
sloping  pile  of  sand,  i  i,  which  has  run  down  from  above. 

This  fine  example  of  a  gravel  bluff  simply  illustrates  what 
may  be  found  on  almost  every  square  mile  of  the  northern  states. 
This  view  is  129  feet  above  the  bed  of  the  Huron  River,  and  204 
feet  above  the  bed  rock,  which  has  only  been  reached  by  boring. 
On  the  bed  rock  the  Drift  is  found  to  be  a  heavy  mass  of  unstrat- 
ified  clay,  with  many  large  bowlders  dispersed  through  it.  At 
other  localities  this  bottom  bowlder  clay  is  found  exposed  at  the 
surface.  Sometimes  the  materials  are  so  firmly  packed  together 
that  digging  in  them  is  difficult.  This  is  the  nature  of  hard-pan. 
When  a  wide  extent  of  hard  pan  or  clay  underlies  a  level  region 
and  is  near  the  surface,  it  arrests  the  downward  escape  of  the 
rains,  and  gives  rise  to  a  marshy  district. 

Hereafter  we  shall  return  to  a  more  careful  study  of  Drift 
arrangement,  and  shall  try  to  ascertain  how  the  materials  were 
produced,  and  how  they  were  spread  so  extensively  over  the 
country. 

EXERCISES.* 

State  some  geological  fact  observed  by  yourself.  What  other  geological 
facts  can  you  mention?  Is  there  any  hill  of  Drift  materials  near  your  resi- 
dence? Is  there  any  hill  not  formed  of  Drift  materials?  State  how  the  Drift 

*To  THE  STUDENT.— The  "Exercises"  in  this  book  are  not  questions  on  the  text 
but  rather  applications  of  the  principles,  and  generalizations  from  facts  stated  in  the 
text.  They  are  intended  to  stimulate  thought.  Some  may  be  too  difficult  to  answer  at 
present — too  difficult  even  for  the  teacher.  Do  not  let  this  produce  any  feeling  of  dis- 


SPRINGS   AND   WELLS.  7 

hill  appears  to  be  made  up.  State  what  cuts  or  excavations  have  been  made 
in  it.  Did  you  observe  any  sort  of  stratification  in  it?  What  is  the  color  of 
the  sand?  Is  the  sand  coarse  or  fine?  Can  you  name  any  hill  or  place  where 
clay  appears?  Does  the  bed  rock  come  to  the  surface  in  your  neighborhood? 
Is  the  bed  rock  reached  in  digging  wells?  If  so,  does  the  water  come  out  of 
the  rock  or  from  the  Drift?  Does  the  bed  rock  belong  to  the  Drift?  Men- 
tion some  valley  which  is  sunken  in  the  Drift.  Mention  some  steep  bank 
along  the  valley.  Mention  a  bank  or  hill  not  covered  by  vegetation.  Where 
is  sand  obtained  for  making  mortar?  What  is  the  difference  between  sand 
and  gravel?  Mention  some  prairie  region.  Is  it  level  or  hilly?  What  sort 
of  material  lies  at  the  surface  of  a  prairie?  Why  does  not  Drift  lie  on  the 
surface  ? 


STUDY   II.— Springs  andWells. 

I  suppose  you  remember  the  little  pond,  where  the  water  rests 
in  a  little  basin  of  earth  and  never  leaks  out  at  the  bottom. 
What  holds  the  water?  If  you  dig  a  hole  in  the  garden  and  fill 
it  with  water,  the  water  soon  disappears.  It  soaks  into  the  ground. 
But  if  you  cover  the  bottom  and  sides  with  a  coat  of  clay,  the 
water  is  retained.  You  may  have  seen  little  duck  ponds  made  in 
this  way.  It  is  a  layer  of  clay  which  holds  the  water  in  the  little 
lakelet  in  the  field.  Clay  is  so  fine  and  compact  that  it  is  almost 
impervious  to  water. 

Suppose  the  little  pond  filled  with  sand  and  gravel.  Now  we 
have  a  basin  of  loose  materials  completely  saturated  with  water, 
and  the  clay  bed  beneath  prevents  the  water  from  escaping.  The 
surface  of  the  materials  is  wet;  the  water  is  stagnant.  After  a 
time  some  decaying  vegetable  matter  may  accumulate  on  it,  and 
grasses  and  sedges  may  take  root,  and  we  shall  have  a  marsh. 
Nearly  all  marshes  and  swamps  are  simply  accumulations  of  sand, 
gravel,  and  soil,  which  are  kept  saturated  with  water  because  a 
bed  of  clay  or  hard  pan  underlies  and  prevents  the  water  from 
soaking  away. 

couragement.  If  you  answer  half  of  these  questions  you  do  well.  With  a  little  reflection 
you  will  answer  more.  It  will  be  all  the  more  useful  if  some  research  is  necessary,  or  if 
the  question  has  to  be  pondered  over  several  days  or  weeks.  He  is  the  most  meritorious 
student,  however,  who  succeeds  in  explaining  the  greatest  number  of  points  presented. 


8 


GEOLOGICAL   STUDIES. 


Of  course  there  is  a  raised  rim  around  this  basin.  From  the 
level  of  the  marsh  the  Drift  surface  slopes  upward  on  all  sides. 
Let  us  now  dig  a  ditch  through  the  Drift  border  of  the  swamp, 
and  give  it  a  slight  descent  toward  the  nearest  stream  of  water. 
Now  the  water  drains  from  the  swamp,  and  the  land  becomes 
sufficiently  dry  for  cultivation.  Now  the  swamp  may  be  plowed 
and  planted  to  corn.  The  basin  of  the  swamp  still  collects  the 
rains,  but  the  ditch  continually  carries  away  the  excess.  If  the 
ditch  were  covered,  we  should  see  the  water  only  at  its  place  of 
exit,  and  we  might  consider  it  a  spring. 

On  the  hill  slope  is  a  spring,  which  is  nothing  but  the  mouth 
of  a  covered  ditch  or  drain  conveying  the  water  from  some 
saturated  bed  of  porous  materials  concealed  beneath  the  fields. 
How  steadily  it  flows!  How  limpid  and  cool  and  refreshing  is  the 
stream!  It  glides  down  the  bank,  and  is  soon  joined  by  several 
other  streamlets  fed  by  other  springs  along  the  same  hill  slope. 
All  together  they  form  a  pretty  little  brook,  which  flows  through 
the  meadows  and  pasture  lands  for  many  a  mile.  And  all  along 
its  course  the  grateful  cattle  slake  their  thirst  from  the  cool 
stream. 


FIG.  8.— SPUING  ISSUING  FROM  A  BANK  OF  DRIFT. 

Let  us  go  back  to  the  hillside  spring.  Here,  Fig.  8,  is  a 
cut  which  shows  the  various  beds  of  sand,  gravel,  and  clay  which 
form  the  Drift  hill  from  which  the  water  issues.  Here  is  the  soil 


SPRINGS   AND   WELLS.  9 

at  the  top  with  its  vegetation,  and  underneath  are  the  common 
Drift  materials  presenting  their  usual  imperfect  stratification, 
their  oblique  lamination,  and  their  abrupt  limitations.  It  is  the 
same  thing  as  seen  in  the  Drift  section  in  Fig.  7.  Only  here  is 
a  bed  of  clay.  It  is  from  the  upper  surface  of  the  clay  that  the 
water  issues.  This  bed  of  clay  extends  back  into  the  hill  an 
unknown  distance.  It  may  be  a  quarter  of  a  mile  or  more.  It 
may  be  even  a  mile  or  several  miles.  Generally,  however,  all  the 
Drift  beds  have  but  very  limited  extent.  Now,  in  this  case,  the 
rain  which  falls  upon  the  fields  percolates  downward  through  the 
sand  and  gravel  beds,  but  is  arrested  by  the  clay  bed.  Then  the 
water  flows  over  the  surface  of  the  clay  bed  in  the  direction  of 
its  slope,  and  that  happens  to  bring  it  to  a  place  of  outcrop  on 
the  hillside.  The  clay  bed  is  like  a  basin  to  hold  the  water,  though 
it  may  be  filled  with  sand.  If  the  basin  is  flat,  or  very  shallow, 
we  have  a  broad  sheet  of  sand  saturated  with  water  ready  to 
flow  off  wherever  its  margin  reaches  a  hill  slope.  If  the  basin  is 
depressed  like  a  trough,  the  most  abundant  flow  is  along  the 
trough.  If  the  hill  slope  cuts  across  the  trough,  then  the  move- 
ment of  the  considerable  stream  may  wash  out  some  of  the  sand, 
and  leave  a  real  underground  passage,  along  which  flows  a  sub- 
terranean stream.  The  case  shown  in  Fig.  8  is  much  like  this. 

Now,  evidently,  if  the  water  basin  extends  back  under  the 
land,  it  is  possible  for  the  farmer  whose  house  is  too  elevated  to 
have  a  spring  to  dig  down  to  the  basin  of  water  which  supplies 
the  spring.  This  is  a  well.  Wherever  an  excavation  is  sunk  to  a 
bed  of  sand  resting  on  a  clay  stratum,  there  water  will  be  found. 
But  no  one  can  tell  certainly  the  depth  at  which  the  cky  stratum 
will  be  reached.  In  some  places  it  is  so  near  the  surface  that 
even  a  common  cellar  reaches  the  water.  In  other  places  it  lies 
at  a  depth  of  fifty,  eighty,  or  one  hundred  feet;  and  the  well 
would  be  too  deep  for  use.  But  remember  that  it  is  not  every- 
where the  same  clay  stratum  which  arrests  the  water.  As  these 
Drift  beds  are  of  very  limited  extent,  no  one  can  be  certain  of 
reaching  water  at  the  same  depth  as  in  another  well  but  a  few 
rods  distant.  Nor  does  the  height  of  the  ground  indicate  any- 


10 


GEOLOGICAL  STUDIES. 


thing  in  reference  to  the  depth   of   the  water-bearing  stratum. 
All   these   things   are  illustrated  in  the  adjoining  cut,  Fig.  9. 


Pitt.  9.— DEEP  AND  SHALLOW  WELLS. 

Here  «,  b,  c  are  clay  beds,  each  of  limited  extent,  and  each  over- 
laid by  a  sandy  bed  which  receives  water  by  percolation  from  the 
surface.  The  descending  water  which  is  arrested  by  c  is  con- 
veyed to  an  outcrop  on  the  hill  slope,  where  it  escapes  as  a  spring 
and  continues  its  descent.  That  which  is  arrested  by  a  and  b 
spreads  laterally,  and  after  the  basins  are  full  it  overflows  and 
descends  to  still  lower  basins.  At  e  the  basin  b  is  reached  by 
digging  ten  or  fifteen  feet.  At  d,  which  is  but  a  few  rods  dis- 
tant, and  is  also  at  a  lower  level,  the  well  must  be  sunk  fifty  feet 
to  reach  the  water  basin  a. 

Probably  the  water  in  basins  a  and  b  finds  outlet  somewhere 
in  springs.  It  may  be  directly  from  these  basins,  or  it  may  be 
from  other  basins  into  which  these  overflow.  The  fact  that  a 
basin  supplies  one  or  many  springs  does  not  prevent  its  supplying 
wells  also.  An  excavation  sunk  at  f  would  result  in  a  well, 
though  the  spring  or  range  of  springs  from  the  basin  c  may  not 
be  far  away. 

Spring  and  well  waters  are  not  absolutely  pure.  Remember 
that  these  waters  came  from  the  surface  of  the  land,  and  must 
have  dissolved  and  carried  away  as  much  as  possible  both  from 


SPRINGS   AN"D    WELLS. 


11 


the  surface  and  from  beneath  the  surface.  You  can  easily  ima- 
gine that  some  well  and  spring  waters  are  notably  impure  and 
unhealthy.  Some  villages  and  cities  have  been  so  poisoned  by 
water  which  seemed  to  possess  a  sparkling  purity  that  deadly 
epidemics  have  been  occasioned.  In  many  an  instance  the  mys- 
terious deaths  of  the  inmates  of  an  isolated  dwelling  —  even  a 
farm  dwelling  in  the  midst  of  the  country  air  —  have  been  traced 
to  impurity  of  well  water  infected  by  drainage  from  the  sur- 
face. Geologically  speaking,  however,  we  are  most  interested 
in  the  mineral  substances  dissolved  by  subterranean  waters  and 
supplied  to  wells  and  springs.  The  most  frequently  occurring 
are  compounds  of  lime  and  iron.  The  Drift  sands  abound  in 
them;  the  waters  dissolve  them,  and  escaping  to  the  surface  re- 
deposit  them.  A  common  compound  of  lime  thus  deposited  is 
of  the  nature  of  chalk  and  limestone.  It  is  deposited  because 
the  water  escaping  to  the  surface  and  relieved  of  its  pressure 
cannot  hold  as  much  as  while  under- 
ground. When  the  deposit  takes  place 
in  standing  water,  it  forms  a  soft, 
white  substance  called  marl.  When 
deposited  over  the  surface  of  dry 
ground,  it  builds  up  a  layer  of  traver- 
tin,  which  is  like  a  rock,  and  in  France 
and  Italy  has  been  employed  exten- 
sively for  building  purposes.  When, 
in  flowing  over  the  surface,  the  deposit 
incrusts  mosses,  leaves,  sticks,  or  bones, 
cementing  them  in  a  stony  mass,  it  is 
commonly  called  calcareous  tufa. 

Iron  deposits  are  formed  in  a  similar 
way.  When  the  iron  compound  saturates  the  materials  of  a 
swamp,  it  forms  bog  iron  ore,  and  may  possess  any  percentage  of 
iron,  according  to  the  copiousness  and  duration  of  the  deposition. 
Bog  ores  in  some  places  exist  in  such  abundance  and  purity  that 
iron  is  manufactured  from  them.  Indeed,  it  is  not  unlikely,  as 
we  shall  see,  that  the  great  workable  beds  of  iron  ore  were 


FIG.  10. — PETRIFIED  Moss. 


12  GEOLOGICAL   STUDIES. 

originally  mere  iron-soaked  bogs.  A  similar  compound  of  man- 
ganese is  sometimes  deposited  in  low  grounds  in  a  similar  way. 
This  product  is  black,  and  is  known  as  wad  or  bog  manganese. 
Both  bog  ores  are  employed  as  paint.  The  bog  iron  gives  us 
ochre,  and  the  bog  manganese  a  black  pigment  much  used  in 
carriage  painting.  Waters  holding  limestone  in  solution  are 
"hard."  Those  holding  iron  are  said  to  be  ferruginous,  and 
often  leave  a  rusty  deposit  on  the  surfaces  which  they  bathe. 
Ferruginous  spring  waters  are  often  described  as  chalybeate. 
Many  of  them  possess  valuable  medicinal  properties. 

EXERCISES. 

Describe  the  situation  of  the  finest  spring  known  to  you.  What  deposits, 
if  any,  does  the  water  leave?  Does  it  produce  any  rusty  stain?  State  where 
some  travertin  or  calcareous  tufa  may  be  found.  When  moss  is  petrified, 
does  the  substance  of  the  moss  necessarily  remain  ?  What  becomes  of  it  if 
not  remaining?  What  is  the  cause  of  the  white  deposit  in  the  bottom  of  the 
tea  kettle  ?  What  sort  of  water  must  be  used  to  prevent  it  ?  What  would  be 
the  effect  of  hard  water  upon  steam  boilers?  Suppose  water  holding  lime- 
stone in  solution  percolates  through  a  bed  of  gravel,  what  happens  to  the  gravel 
after  a  time?  Could  iron  compounds  be  used  to  produce  the  same  result? 
Name  some  well  which  is  much  shallower  than  a  neighboring  well.  Suppose 
the  Drift  were  all  sand,  how  would  the  existence  of  springs  be  affected? 
Where  would  the  surface  water  all  go?  What  would  be  the  effect  on  streams 
of  water?  Mention  a  region  where  the  surface  materials  are  all  sand.  Are 
streams  of  water  plentiful  there  ?  Did  you  ever  hear  of  a  river  disappearing 
in  the  ground?  After  such  a  disappearance  would  it  be  possible  for  the 
river  to  reappear?  Search  on  the  map  of  Asia  or  Africa  and  point  out  rivers 
which  terminate  on  the  land.  Suppose  the  Drift  were  all  clay,  how  would 
the  existence  of  springs  be  affected? 


STUDY   III.— Bowlders. 

Let  us  return  to  the  bowlders.  Except  over  the  prairie 
regions  we  find  them  generally  distributed.  Multitudes  of  them 
may  be  seen  upon  the  surface,  and  almost  every  excavation 
reveals  them  buried  beneath  the  surface  to  depths  as  great  as  are 


BOWLDERS. 


13 


reached  by  the  Drift  formation.  In  limited  districts  the  Drift  is 
restricted  chiefly  to  sand  or  to  clay;  and  the  uses  to  which  bowl- 
ders are  applied  are  diminishing  the  number  in  sight.  Still,  it  is 
no  uncommon  thing  to  see  them  clustered  as  thickly  as  is  shown 
in  Fig.  6.  Bowlders,  in  some  instances,  retain  enormous  dimen- 
sions. Several  notable  cases  have  been  cited  by  the  geologists  of 
New  Hampshire,  and 
one  of  these  is  repro- 
duced in  the  adjoining  il- 
lustration, Fig.  11.  This 
lies  near  Gilsum,  New 
Hampshire.  It  is  46 
feet  long,  24  feet  wide, 
and  26  feet  high.  It  is 
so  large  that  a  country 
school  house  is  almost 
hidden  behind  it.  In 
1817  an  enormous  piece 
was  split  off  by  the  ac- 
tion of  frost.  The  piece 

was  33  feet  long  and  10  feet  wide.  The  whole  stone,  before  the 
splitting,  contained  32,000  cubic  feet,  and  weighed  2,286  tons. 
A  thousand  miles  from  here,  on  the  south  shore  of  Lake  Superior, 
are  other  enormous  bowlders,  some  of  which  are  shown  in  Fig.  12. 
The  larger  one  is  of  porphyry,  and  lies  twenty-five  feet  high. 
As  with  all  bowlders,  its  angles  have  been  rounded  off.  We 
must  endeavor,  in  due  time,  to  ascertain  the  cause  of  this. 
One  of  the  largest  bowlders  known  lies  in  the  Northwest  Ter- 
ritory, north  of  Montana.  It  is  of  quartzite,  and  according  to 
G.  M.  Dawson,  the  portion  above  ground  is  40x40x20  feet. 
Another  one  is  40x30x22  feet. 

One  peculiar  circumstance  connected  with  nearly  all  bowlders, 
large  or  small,  is  their  hardness.  This  is  so  notorious  that,  in 
allusion  to  their  hardness  and  roundness,  they  are  very  generally 
known  as  "hard-heads."  Occasionally  we  find  a  real  bowlder 
soft  enough  to  be  scratched  with  a  knife.  Some,  also,  are  in  a 


FIG.  11.— GREAT  BOWLDER  NEAR  GILSUM,  N.  H. 
(C.  H.  Hitchcock.) 


14 


GEOLOGICAL   STUDIES. 


state  of  progressive  disintegration.  In  the  course  of  time  they 
will  be  reduced  to  sand  and  mingled  with  the  other  constituents 
of  the  soil.  This  suggests  that  many  bowlders  must  already 
have  been  completely  disintegrated,  and  that  the  finer  constit- 
uents of  the  Drift  have  probably  been  derived  from  decaying 
rocks.  It  suggests,  further,  that  if  these  bowlders  were  ever 
angular,  the  simple  process  of  decay  would  have  removed  their 
angles,  and  reduced  them  to  their  present  rounded  forms.  We 
must  keep  this  possibility  in  mind. 


FIG.  12. — GREAT  BOWLDER  OF  PORPHYRY  AT  ST.  IGXACE,  LAKE  SUPERIOR. 

Everyone  has  noticed  the  accumulation  of  bowlders  along 
certain  beaches  and  points  exposed  to  the  action  of  the  waves. 
This  is  not  because  bowlders  are  transported  to  such  situations 
and  laid  down.  It  is  because  the  Drift  abounds  in  bowlders,  and 
in  the  exposed  situations  mentioned,  the  waves  wash  out  the  sand 
and  pebbles,  leaving  the  bowlders  to  settle  together  close  by  the 


BOWLDERS.  15 

water's  edge.  Innumerable  bowlder  points  may  be  seen  along 
the  coast  of  New  England.  One  interesting  example  is  at  Gay 
Head,  on  Martha's  Vineyard.  The  Great  Lakes  exert  a  wave 
action  almost  equal  to  that  of  the  sea,  and  similar  bowlder  beaches 
may  be  witnessed  at  Keweenaw  Point,  Lake  Superior,  at  Point 
Waugoshance,  Lake  Michigan,  and  a  hundred  other  localities. 
The  curious  phenomenon  of  "walled  lakes"  finds  its  explanation 
here.  Many  small  lakes  in  the  northwestern  states  exhibit  a  rude 
sloping  wall  of  bowlders  forming  the  beach  on  one  or  more  sides. 
Human  fancy  has  sometimes  attributed  these  walls  to  the  agency 
of  the  Indians  or  their  predecessors,  or  even  to  a  race  of  giants. 
We  have  only  to  conceive  the  original  sandy  beach  filled  with 
bowlders,  and  the  easily  movable  sand  washed  out  by  the  action 
of  the  waves,  to  understand  that  the  bowlders  would  gradually 
settle  together  into  the  position  of  a  rude  sloping  wall. 

Almost  every  neighborhood  in  the  northwestern  states  is  in 
possession  of  one  or  more  pieces  of  metallic  copper  discovered  in 
the  Drift.  These  are  real  bowlders.  They  bear  the  same  evi- 
dences of  wear  as  the  stones.  They  have  apparently  been  sub- 
jected to  the  same  ordeal  as  the  other  constituents  of  the  forma- 
tion of  which  they  are  a  part.  These  are  examples  of  native 
copper.  But  native  copper  is  not  known  to  exist  in  all  the  coun- 
try except  in  the  region  of  Lake  Superior.  As  it  would  not  seem 
reasonable  to  regard  these  Drift  specimens  as  produced  where  we 
find  them,  the  theory  is  suggested  that  they  have  been  brought 
from  Lake  Superior.  Now,  in  the  same  connection  you  must 
have  noticed  that  nearly  all  our  bowlders  are  unlike  any  rocks 
found  in  place  at  points  nearer  than  the  shores  of  the  Upper 
Lakes.  All  these  indications  point  toward  the  far  north  as  the 
region  whence  our  Drift  materials  have  been  derived.  We  may 
further  conclude  that  they  would  not  have  been  transported  from 
the  far  north  without  exposure  to  much  wear,  which  would  have 
reduced  their  volume,  rounded  their  angles,  and  produced  an 
abundance  of  fine  material.  These  inferences  must  be  borne  in 
mind  when  we  come  to  theorize  about  the  agency  which  effected 
the  transportation  of  so  enormous  a  quantity  of  stones  and  sand. 


16  GEOLOGICAL   STUDIES. 

A  more  attentive  inspection  of  particular  bowlders  shows  that 
very  few  are  entirely  homogeneous.  You  must  by  all  means 
make  the  examination  for  yourself.  A  good  many  presenting  a 
light-colored  or  pinkish  appearance  are  nearly  homogeneous; 
but  most  of  these,  on  close  inspection,  seem  to  be  formed  of 
grains  more  or  less  closely  compacted  together;  and  they  contain, 
also,  an  occasional  grain  or  streak  or  blotch  of  a  different  color. 
Some  dark-bluish  or  blackish  bowlders  also  appear  to  the  naked 
eye  as  almost  homogeneous.  Close  inspection,  however,  espe- 
cially with  a  magnifier,  shows  that  they  are  finely  granular. 
Most  of  these  reveal,  also,  a  stratified  structure;  that  is,  lines  or 
streaks  or  bands  of  slightly  varying  character  extend  in  parallel 
directions  across  the  surface  of  the  stone.  They  indicate  that 
the  whole  stone  is  composed  of  layers  or  strata  which  slightly 
differ  from  each  other  in  color  or  fineness. 

Most  of  the  bowlders,  however,  are  distinctly  heterogeneous  in 
constitution.  This  is  shown  by  the  different  colors  of  the  mate- 
rials. Generally  each  different  color  indicates  a  different  mineral. 
Most  bowlders  contain  two  or  three  different  minerals,  as  you 
will  immediately  observe.  Some  contain  even  more.  Now,  the 
name  of  a  rock  depends  on  the  minerals  of  which  it  is  composed. 
Hence,  to  determine  the  minerals  must  be  our  first  study.  If  the 
minerals  are  promiscuously  and  somewhat  equally  distributed, 
the  rock  is  not  stratified;  it  is  massive.  Unequal  distribution 
sometimes  exists  in  a  massive  rock,  but  the  materials  are  not  dis- 
posed in  parallel  planes.  When  they  are  so  disposed  we  may 
know  the  rock  is  stratified.  But  these  various  layers  are  not  to 
be  taken  as  strata;  they  are  laminae  if  they  cohere  together. 
Strata  are  indicated  by  the  separation  of  a  rock  into  distinct 
beds.  If  the  strata  are  nearly  a  foot  thick  or  over,  the  rock  is 
thick-bedded.  We  shall  use  the  term  schistose  for  thin-bedded 
rocks.  The  lamination  of  a  rock  is  often  in  the  same  direction  as 
the  bedding  or  stratification;  but  sometimes  it  crosses  the  bed- 
ding. Besides  the  minerals  which  make  up  the  principal  bulk  of 
the  rock,  you  will  often  discover  one  or  more  other  kinds  to  a 
sparing  extent.  These  minerals  differ  generally  in  color  and  also 


BOWLDERS.  17 

in  lustre,  transparency,  hardness,  and  crystalline  form.  What 
we  mean  by  lustre  will  be  understood  when  you  compare  a  piece 
of  glass  with  pearl  or  polished  steel.  The  broken  surface  of  the 
glass  reflects  light  perfectly,  brilliantly.  A  reflecting  surface  of 
pearl  is  less  perfect;  the  light  from  it  is  softer.  As  to  lustre,  the 
glassy,  the  pearly,  and  the  metallic  are  the  most  important  dis- 
tinctions to  make.  Some  minerals,  also,  are  transparent,  like 
glass;  others  are  translucent,  permitting  light  to  pass  imper- 
fectly, though  nothing  can  be  definitely  seen  through  them. 
Others  are  opaque.  In  ordinary  bowlders  nearly  all  the  minerals 
are  hard,  but  with  a  tester  you  will  readily  discover  that  some  are 
more  easily  scratched  than  others,  and  some  cannot  be  scratched 
at  all.  As  to  crystalline  form,  nothing  can  be  made  out  in  some 
cases;  but  in  others  we  can  discern  a  line  or  an  angle,  or  a  plane, 
if  nothing  more.  Even  so  much  indicates  that  a  crystalline  form 
belongs  to  the  mineral,  and  often  gives  a  very  important  clew. 

There  is  one  other  particular  in  which  minerals  differ  from 
each  other.  It  is  very  important,  but  the  distinctions  generally 
cannot  be  detected  without  making  experiments  too  nice  and 
elaborate  for  us  to  undertake.  They  differ  in  chemical  composi- 
tion. The  ultimate  substances  of  which  they  are  composed  are 
different  in  the  relative  proportions  in  which  they  exist.  One 
simple  test  may  always  be  applied  by  us;  we  may  observe 
whether  effervescence  is  caused  by  an  acid;  but  beyond  this  we 
must  take  the  statements  of  the  chemists  who  have  the  requisite 
appliances  for  making  chemical  analyses.  Accomplished  mineral- 
ogists must  themselves  be  chemists;  and  it  is  their  practice  to 
employ  an  outfit  more  or  less  portable  for  making  analyses  in  the 
dry  way /  that  is,  without  making  a  solution  of  the  mineral  to  be 
tested.  They  make  use  of  a  How-pipe  and  mostly  dry  re-agents, 
in  the  flame  of  a  lamp  or  gas  jet.  But  though  we  cannot  under- 
take analyses  for  ourselves,  it  is  indispensable  to  understand 
something  of  the  chemical  constitution  of  minerals;  and,  there- 
fore, before  we  proceed  farther  we  must  explain  the  rudimentary 
principles  of  chemistry. 


18  GEOLOGICAL   STUDIES. 


EXERCISES. 

What  very  large  bowlder  have  you  ever  seen?  What  is  its  color  as  nearly 
as  you  remember?  Is  it  homogeneous,  or  is  it  composed  of  different  min- 
erals? Have  you  ever  noticed  the  distinction  between  stratified  and  unstrat- 
ified  bowlders?  Here  are  fragments  of  rocks  obtained  by  breaking  up 
several  different  sorts  of  bowlders;  pick  out  one  which  is  homogeneous. 
Pick  out  one  which  is  heterogeneous.  How  many  kinds  of  minerals  in  the 
last?  Pick  out  one  having  a  massive  structure.  One  having  a  schistose 
structure.  One  with  a  thick-bedded  structure.  Has  the  latter  any  laminae? 
Pick  out  a  specimen  showing  laminae.  What  distinguishes  the  laminae  from 
each  other?  What  different  colors  or  forms  of  minerals  can  you  distinguish 
in  it  ?  Put  all  the  massive  specimens  in  a  pile  together.  Put  all  the  strati- 
fied specimens  together.  Are  there  any  homogeneous  rocks  in  the  last  pile  ? 
[The  teacher  will  frame  a  large  number  of  similar  exercises.] 


STUDY  IV.— A  Little  Chemistry. 

It  is  generally  believed  that  all  matter  is  composed  of  atoms, 
or  portions  so  small  that  they  are  never  divided  and  cannot  be 
divided.  The  finest  dust  floating  in  the  air  is  coarse  in  compari- 
son. The  atoms  are  so  minute  that  they  are  not  only  invisible  in 
a  beam  of  light,  but  also  under  the  most  powerful  microscopes. 
An  impressive  idea  of  their  minuteness  may  be  gained  by  learn- 
ing that  if  a  drop  of  water  could  be  enlarged  to  the  size  of  the 
earth,  the  atoms  of  which  it  is  composed,  each  enlarged  in  the 
same  proportion,  would  be  about  the  size  of  small  shot.  Of  such 
inconceivably  minute  parts  are  all  substances  composed.  Iron, 
stones,  water,  and  air  consist  alike  of  ultimate  atoms. 

Now  let  us  follow  our  chemical  teachers.  Among  these  bill- 
ions of  billions  of  atoms  there  are  held  to  be  about  sixty-four 
different  sorts.  There  is  one  kind  of  atom  in  iron,  another  in 
gold,  another  in  sulphur.  Some  atoms  appear  to  be  much  more 
abundant  than  others.  If  we  take  an  average  sample  of  the  solid 
part  of  the  earth  weighing  one  hundred  pounds,  it  will  be  chiefly 
made  up  of  the  atoms  or  elements  named  below,  and  in  about 
the  proportions  stated  : 


A    LITTLE    CHEMISTRY.  19 


Oxygen  .            .      45  pounds. 

Silicon         .  .            25  " 

Aluminum  .            .10  " 

Iron             .  .              8  " 

Calcium  .                     6 

Sodium       .  .            Si  " 

Potassium  2  ' ' 


Carbon  ~] 

Hydrogen 

Sulphur  I  All    together    nearly 

Nitrogen          |  H  pounds. 

Chlorine 

Magnesium 


In  the  atmosphere  and  in  water  there  are  larger  proportions 
of  Nitrogen,  Oxygen,  and  Hydrogen.  A  vast  number  of  atoms 
of  the  same  kind  brought  together  forms  a  visible  amount  of  the 
substance.  Some  substances  are  solid,  others  are  liquid  or  gaseous 
at  ordinary  temperatures,  and  under  other  ordinary  conditions. 
But  it  has  been  shown  that  heat  will  liquefy,  and  even  vaporize, 
all  solid  substances,  while  cold  and  increased  pressure  will  liquefy, 
and  even  solidify,  all  gases. 

All  the  atoms  have  a  tendency  to  come  into  close  union  with 
other  atoms,  and  to  remain  so  united.  This  tendency  is  com- 
monly known  as  chemical  affinity.  The  union  so  formed  is  a 
chemical  compound.  Nearly  all  the  other  atoms  have  affinity  for 
the  atom  called  oxygen.  The  compound  resulting  from  the  union 
of  oxygen  with  another  element  is  termed  an  oxide.  Thus  iron 
and  oxygen  form  iron  oxide,  or  oxide  of  iron.  Silicon  and  oxy- 
gen form  silicon  oxide  /  aluminum  and  oxygen,  aluminum  oxide. 
So  chlorine,  bromine,  iodine,  and  sulphur  united  with  other  sub- 
stances form  chlorides,  bromides,  iodides,  and  sulphides.  Many 
of  these  compounds  are  commonly  known  by  other  than  their 
chemical  names.  Thus,  one  iron  oxide  is  simple  iron  rust;  hydro- 
gen oxide  is  water;  calcium  oxide  is  lime;  sodium  oxide  is  caustic 
soda;  potassium  oxide  is  caustic  potash;  silicon  oxide  is  silica,  or 
quartz;  sodium  chloride  is  common  salt;  iron  sulphide  is  pyrite. 
Some  compounds  contain  two,  three,  or  more  times  as  much  oxy- 
gen, or  chlorine,  or  sulphur  as  others;  but  we  shall  not  here  ob- 
serve the  distinctions. 

Now,  a  very  important  chemical  principle  is  this :  Oxygen 
united  with  certain  substances  produces  acid-forming  oxides; 
while  with  other  substances  it  forms  basic  oxides.  The  addition 


20  GEOLOGICAL    STUDIES. 

of  hydrogen  to  an  acid-forming  oxide  makes  an  acid.  The  names 
of  the  acids  most  important  for  us  end  in  ic.  Thus,  sulphuric 
acid,  or  "oil  of  vitriol,"  is  composed  of  sulphur,  oxygen,  and  hy- 
drogen. Nitric  acid  is  composed  of  nitrogen,  oxygen,  and  hydro- 
gen. The  basic  oxides  generally  have  names  which  end  in  a. 
Many  of  them  have  also  old,  popular  names,  as  before  stated. 

Another  important  principle  is  this  :  The  acids  have  strong 
tendencies  to  form  compounds  with  the  bases.  Such  compounds 
are  salts /  and  if  the  name  of  the  acid  end  in  ic,  the  name  of  the 
salt  ends  in  ate.  Thus,  sulphuric  acid  and  soda  form  sodium  sul- 
phate, or  according  to  the  old  nomenclature,  still  much  used,  sul- 
phate of  soda.  Silicic  acid  and  lime  form  calcium  silicate,  or 
silicate  of  lime;  carbonic  acid  and  lime  form  calcium  carbonate, 
or  carbonate  of  lime,  which  is  familiarly  known  as  limestone, 
chalk,  and  marl.  The  latter,  however,  commonly  contains  an  ad- 
mixture of  clay. 

A  third  important  principle  is  this:  The  affinities  of  different 
substances  for  the  same  substance  are  not  all  equal.  Sulphuric 
acid,  for  instance,  has  a  stronger  affinity  for  lime  than  carbonic 
acid  has.  Hence,  when  sulphuric  acid  is  brought  into  contact 
with  carbonate  of  lime,  the  carbonic  acid  is  driven  off,  and  the 
sulphuric  acid  takes  its  place,  forming  sulphate  of  lime.  All  the 
mineral  acids  will  do  the  same,  forming  each  its  appropriate  salt 
of  lime.  Even  strong  organic  acids,  like  pure  vinegar  or  acetic 
acid,  will  drive  carbonic  acid  away  from  carbonate  of  lime.  As 
carbonic  acid  is  a  gas  (called  also  carbon  dioxide),  it  assumes  the 
form  of  a  gas  instantly  on  being  compelled  to  dissolve  its  union 
with  the  lime.  The  gas  is  much  more  bulky  than  the  carbonate, 
and,  accordingly,  it  forms  numerous  small  bubbles  with  the  liquid 
acid  which  remains  uncombined.  This  phenomenon  is  called  effer- 
vescence. The  demonstration  of  effervescence,  as  illustrative  of 
this  selective  action  among  acids  and  bases,  is  quite  within  the 
reach  of  our  simple  resources.  Take  a  bit  of  chalk  and  apply  a 
drop  of  any  strong  acid  to  the  surface,  and  effervescence  instantly 
ensues.  The  effervescence  shows  that  carbonic  acid  was  one  of  the 
constitutents  of  the  chalk.  Strong  vinegar  will  produce  efferves- 


A    LITTLE    CHEMISTRY.  21 

cence.  The  same  result  follows  if  marl  or  limestone  is  employed; 
hence,  these  are  shown  to  be  carbonates. 

A  fourth  important  principle  is  this :  Heat  weakens  the  strength 
of  the  union  formed  between  two  or  more  substances.  We  have 
just  seen  that  limestone  is  carbonate  of  lime  —  that  is,  a  union 
between  lime  and  carbonic  acid.  Now,  if  we  subject  limestone 
to  a  red  heat,  the  union  between  the  acid  and  the  base  is  not  only 
weakened,  it  is  destroyed.  The  carbonic  acid  rises  into  the  atmos- 
phere, and  the  lime  remains.  Simple  lime  is  known  as  quick- 
lime, or  caustic  lime.  But,  after  cooling,  it  is  eager  to  regain  a 
supply  of  carbonic  acid,  or  other  acid,  and  it  slowly  absorbs  that 
gas  from  the  atmosphere.  If  we  dissolve  quicklime  in  water,  and 
pour  off  the  clear  fluid  standing  over  the  excess  of  lime,  we  have 
lime-water.  This  eagerly  unites  with  or  neutralizes  any  acid  with 
which  it  comes  in  contact.  Hence  it  is  employed  to  correct 
"acidity  of  stomach."  If  now  we  breathe  into  the  lime-water 
through  a  straw  or  a  g'lass  tube,  the  carbonic  acid  from  the  lungs 
unites  with  the  lime  in  solution  and  forms  a  white  cloud,  because 
the  carbonate  of  lime  resulting  is  not  much  soluble,  and  remains 
as  an  infinitude  of  minute  white  particles.  These  slowly  settle  to 
the  bottom  and  form  a  white,  chalky  powder,  known  as  precipi- 
tated chalk.  This  also  is  used  by  physicians  as  an  antacid. 

Should  we  pour  slowly  a  quantity  of  lime-water  over  a  pile  of 
sand,  it  is  obvious  that  the  carbonate  of  lime  would  be  formed  in 
the  interstices  between  the  particles,  and  might  finally  fill  them 
up.  The  grains  of  sand  would  then  be  firmly  cemented  together 
by  a  calcareous  cement.  We  shall  find  many  rocks  thus  ce- 
mented. The  application  of  a  drop  of  acid  then  produces  slight 
effervescence,  which  reveals  the  nature  of  the  cement. 

Intense  heat  is  capable  of  dissolving  very  many  unions  —  not 
alone  between  acids  and  bases,  but  between  oxygen  and  other 
substances.  It  is  probable  indeed,  that  a  degree  of  heat  is  pos- 
sible which  would  reduce  all  substances  to  their  ultimate  ele- 
ments. In  such  a  heat,  no  compounds  could  exist.  This  state 
of  matter  is  known  as  dissociation  and  the  facts  are  connected 
with  theories  of  the  primeval  condition  of  the  world. 


2%  GEOLOGICAL   STUDIES. 

Thus  it  appears  that  nearly  all  substances  known  to  us  are 
chemical  compounds.  Minerals  are  chemical  compounds,  for  the 
greater  part.  Certain  metals  only,  in  the  native  state,  are  ele- 
mentary or  tmcompounded.  Gold,  silver  and  copper  are  samples, 
but  nearly  all  metals,  as  well  as  other  substances,  have  entered 
into  combinations  as  oxides  or  chlorides,  or  sulphides,  or  carbon- 
ates and  other  salts.  It  is  an  important  fact  that  every  chemical 
compound  tends  always  to  form  crystals  of  the  same  fundamental 
form.  That  is,  it  will  form  solids  always  of  the  same  order  (cube, 
rhombohedron,  hexagonal  prism,  etc.),  and  always  having  the 
sides  so  inclined  to  each  other  as  to  form  the  same  angle.  If 
then,  for  instance,  we  have  learned  by  observation  what  order  of 
geometrical  solids  is  formed  by  calcium  carbonate,  and  also  the 
values  of  the  angles,  and  then  find  an  unknown  mineral  of  the 
same  geometrical  form,  and  having  the  same  angles,  it  is  per- 
fectly safe  to  conclude  that  the  unknown  mineral  is  calcium  car- 
bonate. That  is,  its  chemical  composition  is  shown  by  its  cystal- 
line  form.  In  the  determination  of  minerals,  therefore,  the 
detection  of  the  crystalline  form  is  always  desirable.  By  means 
of  the  form,  the  hardness,  the  color,  the  lustre  and  the  specific 
gravity,  we  may  generally  make  a  determination  of  the  common 
minerals.  Knowing  the  mineral,  we  know  the  chemical  substances 
in  it.  All  that  we  shall  at  present  attempt  is  the  determination 
of  the  common  minerals  entering  into  the  formation  of  the  com- 
mon rocks;  and  we  shall  attempt  this  almost  wholly  by  an  inspec- 
tion of  their  physical  characters. 

EXERCISES. 

What  is  the  acid  in  carbonate  of  potash?  Of  what  is  chloride  of  cal- 
cium composed?  What  is  the  composition  of  lime?  Name  some  substances 
which  are  elementary.  Name  some  containing  oxygen.  Why  cannot  the 
atoms  of  matter  be  seen  under  the  microscope?  Are  the  atoms  infinitely 
small?  Did  you  ever  notice  a  calcareous  incrustation  on  stones  in  a  pond  or 
lake?  How  might  it  be  explained?  Why  is  it  not  a  pure  white,  like  chalk? 
Name  some  acid  which  has  a  strong  affinity  for  lime.  Name  one  having  a 
feebler  affinity.  What  would  be  a  relief  to  acidity  of  the  stomach?  What 
would  result  if  pulverized  marble  were  thrown  into  a  vessel  of  vinegar?  If 


QUARTZ    AND    FELDSPAR.  23 

vinegar  is  acetic  acid,  what  salt  would  be  formed?  If  you  take  one  hundred 
grains  of  the  average  solid  earth,  how  many  grains  of  silicon  might  be  ex- 
tracted from  it?  How  many  grains  of  potassium?  State,  if  you  can,  what 
elements  are  most  abundant  in  vegetation.  What  is  the  principal  source  of 
carbon  in  plants? 


STUDY  V.—  Quartz  and  Feldspar. 

We  are  now  prepared  to  begin  the  investigation  of  common 
minerals.  Let  us  select  a  common  bowlder  and  break  it  into  so 
many  pieces  that  each  of  us  shall  have  one  fragment  of  conven- 
ient size  to  hold  in  the  hand  and  inspect.  The  collection  of  these 
specimens  may  have  been  done  beforehand;  or  we  may  proceed 
together  to  the  field  and  procure  the  specimens  as  we  need  them. 
The  best  bowlder  to  begin  on  will  be  one  containing  several  min- 
erals. This  will  be  indicated  by  the  various  colors  —  though 
sometimes  various  colors  result  merely  from  different  varieties  of 
the  same  mineral,  as  we  shall  see. 

Now,  with  our  specimens  in  hand,  suppose  one  or  more  of  the 
minerals  is  nearly  white;  and  suppose  another  reddish,  and  an- 
other quite  dark  colored.  Look  attentively  at  the  light  colored 
minerals  and  consider  if  they  seem  to  be  all  alike.  Test  the  hard- 
ness of  several  samples  of  the  white  mineral,  or  minerals.  Can 
you  make  a  scratch  on  them  ?  Yes,  you  say,  your  implement 
leaves  a  dark  metallic  mark.  That  is  not  a  scratch  of  the  min- 
eral. It  shows  that  the  mineral  is  harder  than  the  implement, 
Well  as  soon  as  we  observe  this  we  may  pronounce  the  mineral 
quartz.  This  is  the  hardest  of  all  the  common  minerals.  It  is 
also  very  abundant.  It  is  not  always  white,  or  nearly  white.  It 
may  be  transparent,  pink,  red,  smoky,  or  even  almost  black.  But 
its  hardness  will  always  betray  its  character. 

It  has  another  character  by  which  you  may  almost  always 
detect  it.  Quartz  has  a  vitreous  or  glassy  lustre.  This  is  most 
conspicuous  where  the  quartz  is  transparent,  but  in  all  ordinary 
quartz  the  glassy  lustre  can  be  seen. 


24  GEOLOGICAL   STUDIES. 

The  quartz  minerals  thus  detected  in  the  bowlder  you  find  to 
be  generally  rounded  grains  or  pebbles.  Sometimes,  indeed,  they 
are  so  closely  compacted  together,  that  the  outlines  of  the  grains 
can  scarcely  be  traced.  One  would  think  that  some  larger  quartz 
rock  had  been  reduced  to  small  fragments,  and  the  fragments 
rubbed  together  until  the  angles  were  rounded,  and  then  all  com- 
pacted as  we  see  them.  But  quartz  being  a  simple  mineral,  it 
crystallizes  in  a  definite  form.  The  separate  crystalline  bodies 

resulting  are  crystals.  The  crystal 
of  quartz  is  a  hexagonal  prism. 
Here,  in  Fig.  13,  you  have  a  view  of 
several  crystals,  larger  and  smaller. 
Each  has  six  sides,  and  the  end 
slopes  correspond  to  the  sides  or 
faces.  This  is  the  termination.  Not 
unfrequently  quartz  crystals  occur 
with  a  termination  at  each  end.  The 
crystal  appears  to  have  been  formed 
by  progressive  additions  on  all  the 
FIG.  13.-AGROUPOFCKY8TALS  sides ;  for  almost  always  we  see  one 

side    more    built    out    than    others. 

But  the  more  a  side  projects  the  narrower  it  is,  since  the  con- 
tiguous sides  must  be  preserved  in  true  planes.  Good  quartz 
crystals  may  sometimes  be  found  in  coarse  bowlders,  especially  in 
cavities. 

Pure  quartz  is  transparent,  like  glass,  and  the  crystals  pre- 
sent, therefore,  a  remote  resemblance  to  diamonds.  "  Brazilian 
pebbles"  and  "Alaska  diamonds"  are  merely  crystalline  quartz. 
Quartz,  however,  is  more  commonly  mixed,  with  some  impurity, 
and  it  thus  loses  transparency  and  acquires  color.  Violet  colored 
quartz  is  amethyst.  Quartz  so  mixed  as  to  have  a  uniform  waxy 
lustre  rather  than  a  brilliant,  glassy  lustre  is  chalcedony  •  while 
alternating  bands  of  differently  colored  chalcedony  form  agate. 
A  chalcedony  containing  minute  mossy  patches,  of  deeper  color, 
is  a  moss  agate.  If  the  impurities  greatly  dull  the  lustre  of  the 
quartz  it  becomes  flint,  and  if  they  produce  an  earthy  lustre  it  is 


QUARTZ    AND    FELDSPAR.  25 

jasper  —  red,  black,  or  green.  Chert  is  an  impure  quartz,  gen- 
erally containing  lime. 

It  is  most  important  to  know  of  what  quartz  is  composed.  It 
is  its  composition  which  determines  all  its  properties.  The  chem- 
ist tells  us  that  quartz  is  pure  silica,  and  that  silica  is  composed 
of  silicon  and  oxygen.  There  are  twenty-eight  grains  of  silicon  to 
every  thirty-two  of  oxygen.  So  you  can  calculate  from  the  table 
in  Study  IV  that  one  hundred  pounds  of  the  solid  earth  contain 
about  fifty-three  and  six-tenths  pounds  of  silica,  or  quartz. 

Now  we  will  carefully  examine  and  test  every  part  of  the 
rock  specimen  in  hand,  to  ascertain  whether  it  contains  more 
than 'one  variety  of  quartz.  Very  likely  we  shall  discover  two 
varieties  —  one  with  more  color  than  the  other.  One  may  be 
nearly  transparent,  and  the  other  a  little  reddish  or  a  little  duskv. 
But  we  must  be  sure  the  glassy  lustre  is  also  present. 

Is  there  a  light-colored  mineral  present  which,  with  consider- 
able effort,  receives  a  scratch  ?  Is  there  a  pinkish,  reddish,  or 
cream-colored  mineral  which  can  be  scratched?  Any  mineral  of 
these  colors,  if  so  hard  as  to  be  scratched  with  difficulty,  is  proba- 
bly a  feldspar.  Quartz  will  scratch  feldspar;  but  feldspar  will 
not  scratch  quartz.  Quartz  will  always  scratch  glass.  Most  glass 
may  also  be  scratched  by  feldspar,  but  not  so  readily. 

There  is  sometimes  difficulty  in  deciding  whether  a  small 
grain  of  a  mineral  is  quartz  or  feldspar.  We  had  better  select 
rocks  at  first  which  are  coarse-grained.  But  sometimes  we  are 
compelled  to  make  the  determination  in  a  fine-grained  rock. 
Whether  fine  or  coarse,  we  may  proceed  next  to  examine  the 
lustre.  Feldspar  has  a  pearly  or  subvitreous  lustre  in  most  cases. 
If  we  detect  such  a  lustre  instead  of  the  bright,  glassy  reflection 
caused  by  quartz,  the  question  is  decided.  If  we  have  a  doubtful 
mineral,  we  must  frequently  glance  at  the  lustre  of  an  undoubted 
fragment  of  quartz,  and  compare  the  two  lustres.  Very  often 
the  lustre  serves  to  identify  feldspar. 

But  there  is  another  method.  Feldspar  fragments  often  pre- 
sent in  the  rock  distinct  flat  faces  or  surfaces.  Quartz  fragments 
do  not.  Hence,  if,  on  changing  the  position  of  the  stone  in  ref- 


26  GEOLOGICAL   STUDIES. 

erence  to  the  light,  we  see  here  and  there  bright,  flat  surfaces 
appearing  and  disappearing  as  they  reflect  and  cease  to  reflect 
the  light  from  a  window,  then  we  may  be  pretty  certain  we  have 
feldspar.  If,  on  testing  for  hardness,  one  of  these  appears  a  very 
little  softer  than  quartz,  the  suspicion  is  confirmed.  Still  further, 
if  the  reflecting  plane  is  bounded  by  a  straight  line,  and  another 
plane  or  face  can  be  seen  making  nearly  a  right  angle  with  the 
first  one,  then  we  have  a  final  proof,  if  the  other  indications 
agree,  that  the  mineral  fragment  under  consideration  is  feldspar. 
Here  in  the  margin  is  a  cut  of  a  feldspar  fragment, 
where  a  is  one  of  the  reflecting  faces  and  b  is  the 
other;  and  these  join  together  at  a  right  angle,  or 
FIG  14  nearly  that.  This  is  larger  than  most  of  the  frag- 

FRAGMENT  or       ments  found  in  the  rocks.     A  common  form  under 
which  feldspar  is  seen  is  that  of  a  box  partly  crushed 
by  pressure  applied  in  the  middle  of  one  end  at  the 
top  and  exerted  toward  the  opposite  end  of  the  bottom.     Here 
the  sides  remain  at  right  angles  with  the  top  and  bottom.     But 
such  forms  can  only  be  seen  in  fragments,  and  generally  with  a 
magnifier. 

It  is  often  the  case  that  no  right  angle  can  be  detected.  Still, 
the  reflecting  surfaces  may  be  present,  showing  also  the  pearly  or 
subvitreous  lustre.  But  if  no  faces  can  be  found,  the  pearly 
lustre  may  be  there,  distinctly  less  brilliant  than  in  a  case  of 
broken  quartz;  and  finally,  the  test  for  hardness  remains  to  apply. 
The  test  of  weathering  is  also  valuable.  On  the  weathered  sur- 
face the  quartz  grains  retain  their  glassy  lustre;  feldspar  grains 
weather  opaque  and  earthy,  with  increased  whiteness.  In  spite 
of  these  various  resorts  the  learner  will  sometimes  feel  in  doubt 
whether  certain  fragments  are  quartz  or  feldspar.  This  is  no 
good  reason  for  discouragement.  Quite  possibly  the  case  is  a 
difficult  one.  He  may  try  another  rock,  and,  if  possible,  a  coarser 
one;  or  he  may  keep  on  repeating  the  round  of  tests,  and  come 
to  the  best  decision  he  can. 

The  geometrical  form  under  which  common  feldspar  crystallizes 
is  shown  in  Fig.  15.  Here  you  see  the  position  of  the  right 


QUAKTZ    AND    FELDSPAR. 


27 


ORTHOCLASE,  A  SPECIES  OF 
FELDSPAR. 


angle  represented  in   Fig.  14,  since  II  is  at  right  angles  with  I  i 
and  also  with  0. 

We  say  this  is  common  feldspar;  since 
there  exist  really  several  species  of  feld- 
spars, all  of  which  are  composed  chemi- 
cally of  silica,  alumina,  and  an  alkaline 
constituent,  while  they  differ  according  to 
the  nature  of  that  constituent.  If  to  silica 
and  alumina  be  united  potash,  the  feldspar 
is  orthoclase,  or  common  feldspar,  the  spe- 
cies which  gives  us  most  nearly  a  right 
angle.  This  is  also  called  potash  feldspar. 
If  the  alkaline  constituent  be  soda,  we  FIG.  is.— LARGE  CRYSTAL  OP 
have  the  feldspar  known  as  albite,  or  soda 
feldspar.  If  it  is  lime,  we  get  anorthite. 
If  it  is  soda  and  lime,  we  have  a  soda-lime  feldspar,  labradorite, 
or  oligoclase.  There  are  a  few  other  feldspars,  but  we  need  not 
mention  them  here. 

It  is  important  to  notice  the  proportions  of  silica  in  the  sev- 
eral feldspars,  because  acidic  feldspars,  or  those  with  much  silica, 
are  found  in  company  with  other  minerals  having  much  silica,  and 
basic  feldspars,  or  those  poor  in  silica,  seek  the  company  of  other 
basic  minerals.  Now  the  acidic  feldspars  have  silica  as  follows: 
orthoclase,  65  per  cent ;  albite,  68  ;  and  oligoclase,  62  per  cent. 
The  basic  feldspars  have  silica  as  next  follows:  labradorite,  52; 
anorthite,  43.  (See  the  Table  of  Compositions,  Study  VIII.) 

You  perceive  that  the  feldspars  differ  in  their  composition ; 
but  -we  cannot  easily  test  the  composition,  and  therefore  we  have 
no  certain  way  for  distinguishing  them.  Hence,  sometimes  we 
must  simply  say  the  mineral  is  a  feldspar.  If  we  detect  the  right 
angle,  we  may  say  it  is  orthoclase.  All  the  other  feldspars 
named  may  be  grouped  as  plagioclase  or  triclinic  feldspars.  Of 
the  plagioclase  feldspars,  albite  inclines  to  snowy  white;  anor- 
thite is  often  glassy  and  transparent;  labradorite  inclines  to 
gray,  brown  or  greenish,  with  sometimes  a  beautiful  play  of  colors 
in  reflected  light;  oligoclase  is  generally  white  with  a  greenish 


GEOLOGICAL   STUDIES. 


tinge  and  fine  striae  on  the  principal  faces  —  to  be  seen  with  a 
magnifier.  The  presence  of  the  colors  indicated  affords  only  a  first 
presumption  as  to  the  species  of  plagioclase  under  investigation. 
Any  plagioclase  may  show  striations.  We  may  safely  say:  If  the 
right  angle  is  present,  the  feldspar  is  orthoclase;  if  stride  are 
present  it  is  a  plagioclase;  if  the  feldspar  is  glassy  it  is  very 
probably  a  plagioclase;  if  it  is  cream-colored  or  reddish  it  is 
probably  orthoclase;  if  dusky  or  greenish,  or  with  internal  reflec- 
tions, it  is  probably  plagioclase.  Orthoclase,  also,  undergoes  less 
change  from  weathering  than  plagioclase;  and  it  is  found  more 
commonly  in  the  company  of  quartz. 

Here  is  a  table  in  which  the  characters  are  presented  another 
way: 


Name  of  Feldspar. 

Alkaline 
Constituent. 

Leading  Colors. 

Transparency. 

Orthoclase. 

Potash. 

White,  creamy,  gray,  flesh- 
red. 

Translucent,   opaque. 
Rarely  transparent. 

Microcline. 

Potash—  Soda. 

Like  orthoclase,  or  green. 

Translucent.. 

•d 
.J.  w 

'  Albite. 

Soda. 

White  rarely  bluish,  gray, 
reddish,  greenish. 

Transparent  to  snbtrans- 
lucent. 

«fl 

Oligoclase. 

Soda—  Lime. 

Faintly    grayish-green, 
white. 

Transparent  to  subtrans- 
lucent. 

!!• 

Labradorite. 

Lime  —  Soda. 

Gray,   brown,   greenish. 
Play  of  colors. 

Transparent  to  subtrans- 
lucent. 

E| 

.  Anorthite. 

Lime. 

White,  grayish,  reddish. 

Transparent  to  translu- 
cent. 

By  the  decomposition  of  the  feldspars  we  get  kaolin,  which 
consists  chiefly  of  silica,  alumina  and  water.  It  is  white  when 
pure,  and  is  used  in  the  manufacture  of  porcelain  and  china 
ware. 

EXERCISES. 

Have  you  found  any  quartz  in  the  specimen  in  your  hand?  How  many 
varieties  of  quartz  in  the  specimen?  State  the  color  of  each  variety.  Is  there 
any  transparent  quartz  in  the  specimen?  Point  out  any  feldspar  in  the 


DARK-COLORED    MINERALS.  29 

specimen.  How  do  you  know  it  is  not  quartz?  What  indication  that  it  is 
orthoclase  or  oligoclase?  Point  out  some  reflecting  faces  of  feldspar.  Have 
you  met  with  any  striated  feldspar?  Take  another  bowlder  fragment  and 
point  out  the  quartz.  Point  out  the  feldspar.  How  many  varieties  of  quartz 
can  you  find  in  it?  How  many  varieties  of  feldspar?  Point  out  plagioclase 
if  any.  Practice  holding  different  specimens  in  such  way  as  to  catch  the 
feldspar  reflections.  Notice  again  and  again  the  difference  between  the  lus- 
tre of  feldspar  and  that  of  quartz.  Search  many  different  specimens  from 
different  bowlders  for  varieties  of  feldspar,  and  particularly  for  striated  feld- 
spars. Do  you  often  find  orthoclase  and  plagioclase  in  the  same  bowlder? 
What  are  commonest  colors  of  feldspar,  according  to  your  observation? 
Does  quartz  break  with  smooth  faces,  like  feldspar?  Which  has  the  most 
glistening  lustre?  Have  you  noticed  feldspar  fractures  with  a  dull  lustre? 

OBSERVATION. — The  discrimination  of  feldspar  from  qnartz  is  sometimes  difficult  in 
small  grains.  But  do  not  be  discouraged,  for  it  is  difficult  sometimes  even  for  the  pro- 
fessor. Repeat  these  and  similar  exercises  very  many  times.  Use  the  same  bowlder  frag- 
ments and  also  different  ones.  Every  time  you  succeed  you  will  feel  fresh  delight. 
Every  time  you  fail,  form  a  new  resolve.  Always  study  with  specimens. 


STUDY  VI.— Dark -Colored  Minerals. 

Let  us  examine  farther  the  same  rock  specimens  as  before  used. 
We  suppose  these  contain  one  or  more  dark-colored  minerals.  If 
they  do  not,  we  must  provide  ourselves  with  specimens  from 
some  other  bowlder.  Among  dark  minerals  disseminated  through 
bowlders,  it  will  be  noticed  that  some  occur  in  thin,  mostly  shin- 
ing, scales,  and  others  do  not.  Let  us  take  specimens  containing 
a  scaly  mineral.  It  is  probably  mica.  With  a  knife  point  you 
may  lift  up  a  succession  of  thin  scales  from  the  same  fragment. 
There  seems  no  limit  to  the  capability  of  splitting.  Notice  that 
if  the  surfaces  are  brilliant,  the  scales  are  generally  elastic  and 
tough.  But  examples  long  exposed  to  water  and  air  have  mostly 
lost  their  elasticity,  and  have  become  softer,  sometimes  easily 
crushing  to  a  greenish-gray,  lustreless  powder.  When  the  mica 
is  unaltered  there  is  no  difficulty  in  identifying  it;  but  when 
much  altered  it  approaches  the  appearance  of  some  other  altered 
minerals. 

Mica,  like  feldspar,  is  a  generic  name;  but  all  the  micas  are 


30  GEOLOGICAL   STUDIES. 

composed  of  silica,  alumina,  potash  and  iron,  with  some  other 
characterizing  constituent.  Common  mica  (so-called)  is  the 
species  muscovite.  It  splits  into  thin,  tough,  flexible,  elastic 
scales.  In  color  it  varies  from  white  to  gray,  brown  and  pale 
green.  It  is  sometimes  violet,  yellow  or  dark  olive  green. 
Bronzy  muscovite  is  sometimes  mistaken  by  the  ignorant  for 
gold.  The  transparent  variety  is  extensively  employed  in  stove 
doors,  and  is  sometimes  ignorantly  called  "  isinglass."  By  absorp- 
tion of  water,  muscovite  undergoes  the  changes  already  men- 
tioned, and  becomes  hydromica,  also  called  margarodite.  We 
find  the  mineral  in  all  stages  of  transition  to  hydromica;  and  one 
is  often  at  a  loss  to  decide  between  the  two  names.  Through 
the  same  kind  of  change  it  approaches  talc  and  chlorite,  as  we 
shall  see. 

Deep  black  mica  with  splendent  lustre  is  generally  the  species 
called  biotite.  We  shall  find  it  more  common  than  muscovite. 
Phlogopite  is  yellowish-brown,  brownish,  red  (often  with  copper- 
red  reflections),  green,  white  or  colorless.  This,  also,  is  quite  com- 
mon. Lepidolite  or  lithia-mica  is  sometimes  seen  in  delicate 
pinkish  scales.  You  will  endeavor  to  find  in  bowlders  the  differ- 
ent species  of  mica  mentioned. 

While  speaking  of  the  scaly  minerals  in  our  hands,  it  is  best 
to  mention  a  few  which  are  not  micas.  We  shall  meet  with  them 
occasionally.  Those  which  we  shall  mention  are  all  hydrous 
silicates  of  magnesia,  except  one,  with  generally  other  constitu- 
ents; one  of  these  is  talc,  which  is  simply  a  hydrous  silicate  of 
magnesia  —  that  is,  composed  of  silica,  magnesia  and  water. 
The  scales  are  thin  and  tender,  and  not  elastic,  and  their  color 
ranges  from  apple-green  to  white  or  silvery.  Talc  is  the  softest 
of  the  minerals.  The  scales  are  very  easily  reduced  to  powder. 
The  mineral  has  a  peculiar  greasy  feel,  and  this  is  one  means  of 
distinguishing  it  from  some  micas;  though,  as  before  stated, 
hydromica  approaches  it.  Another  mineral  called  pyrophyllite 
is  a  hydrous  silicate  of  alumina.  Thin  scales  appear  much  like 
talc;  but  the  mineral  is  chiefly  known  as  the  constituent  of  a  fine 
compact  rock  used  for  slate  pencils.  Serpentine,  a  hydrous  silicate 


DARK-COLORED    MINERALS.  31 

of  alumina,  magnesia  and  iron,  is  sometimes  scaly  or  foliated,  but 
more  frequently  fibrous.  It  is  far  better  known,  however,  in  the 
massive  state  as  a  rock.  Its  color  is  leek-green  or  blackish-green, 
and  like  talc  it  has  a  greasy  feel.  Under  chlorite  are  included 
chiefly  two  foliated  minerals  which  are  both  hydrous  silicates  of 
alumina,  magnesia  and  iron,  and  both  of  a  greenish  color.  Of 
these,  ripidolite  is  transparent  or  translucent,  with  flexible,  some- 
what elastic  leaves,  and  prochlorite  is  translucent  or  opaque,  with 
flexible  and  inelastic  leaves.  Keep  a  watch  for  these  scaly  min- 
erals. 

This  ends  the  important  scaly  or  foliated  minerals.  There  are, 
however,  two  species  of  dark  minerals  of  much  importance,  and 
sometimes  we  experience  difficulty  in  distinguishing  them  from 
dark  mica.  Amphibole  is  one  of  these.  If  you  take  in  hand 
a  bowlder  fragment  containing  some  dark  min- 
eral which  is  not  mica,  the  mineral  is  likely  to 
be  hornblende,  the  common  variety  of  amphi- 
bole.  We  can  easily  provide  ourselves  with 
samples  of  such  a  rock.  We  must  have  them. 

Now  look  at  this  dark  mineral,  hornblende.     It     FlG-  ^.-CRYSTALS 

•  t    •    i  °F   HORNBLENDE, 

is  dark  greenish  or  nearly  black,     it  has  a  bright       THE  COMMON  VA- 

lustre,  and  about  the  hardness  of  feldspar.  If  RIETT  or  AMPHI- 
you  scratch  it,  the  streak  is  white  or  whitish. 
You  can  generally  detect  a  crystalline  face;  and  sometimes  you 
find  a  crystalline  form  which  is  like  a  six  or  four  sided  rod,  as 
shown  in  Fig.  16.  Often  the  surface  of  the  crystal  fragment  pre- 
sents a  fibrous  structure.  This  distinguishes  it  from  black  mica. 
Another  variety  of  amphibole  is  white  and  fibrous,  and  this 
is  tremolite  or  asbestos.  Asbestos  somewhat  resembles  linen,  and 
may  be  made  into  cloth  which  is  incombustible.  It  is  used  as  a 
non-conductor  of  heat  to  wrap  around  steam  boilers  and  pipes. 
Still  another  variety  is  actinolite,  consisting  of  coarser  and 
solider,  green  radiating  fibres  or  blades.  Silica,  magnesia,  lime, 
iron,  and  often  alumina  are  the  principal  constituents  of  amphi- 
bole. By  combining  with  water,  hornblende  changes  to  a  soft, 
greenish  mineral  resembling  hydromica,  though  not  in  scales. 


32  GEOLOGICAL   STUDIES. 

The  other  important  species  of  the  dark  minerals  is  pyroxene, 
It  closely  resembles  amphibole,  though  inclining  more  to  green- 
ish tints.  It  holds  the  same  constituents,  though  in  different 
proportions;  and  has  nearly  the  same  crystalline  forms  and  hard- 
ness and  nearly  the  same  specific  gravity.  It  is  not  easily  distin- 
guished without  microscopic  or  chemical  study.  In  colors,  when 
it  varies  from  green  or  greenish-black  (ciugite^  the  common  vari- 
ety), it  approaches  whitish  in  one  direction  (saklite)  and  brown- 
ish in  the  other  (diallage).  It  is  seldom  quite  black,  while  this 
is  a  common  color  with  amphibole  (in  hornblende).*  The  differ- 
ent natures  of  hornblende  and  augite  are  shown  by 
the  fact  that  hornblende  is  very  often  found,  like 
rnuscovite,  in  company  with  quartz,  while  augite  is  sel- 
dom so  found.  Their  resemblance  in  crystalline  form 
will  be  seen  by  comparing  Fig.  17  with  Fig.  16. 
FIG.  17.  Here  the  faces  1 1  make  with  each  other  an  angle 
CBTSTAL  or  of  87°  5',  while  in  hornblende  the  same  faces  stand  at 

THE^OMMON     ^    ^^    °f     124°    3°'-         In    F1g'    1?    thiS     ^^    Is     trUn' 

VARIETY  op    cated  by  the  plane  i  i.     It  is  seldom,  however,  that 
we   can    detect    the    angles    in    the    small    fragments 
found  in  common  rocks. 

There  are  still  two  minerals,  generally  dark,  or  even  black, 
which  possess  some  importance  as  rock  constituents.  One  of 
these  is  tourmaline.  It  is  seldom  sufficiently  abundant  to  deter- 
mine the  name  of  a  rock,  but  its  presence  sometimes  necessitates 
a  qualifying  epithet.  Tourmaline  may  often  be  seen  in  the  form 
of  straight,  stick-like,  shining,  black,  imperfectly  three-sided 
prisms  imbedded  in  crystalline  limestones  or  quartz  rocks,  and 
not  unfrequently  other  kinds  of  rocks.  The  common  prisms 
range  in  size  from  a  twentieth  of  an  inch  to  half  an  inch  and 
over.  Their  sides  are  curved  and  generally  striated  or  fluted, 

*  In  addition  to  this,  augite  is  frequently  found  altered  to  hornblende.  In  spite  of 
these  resemblances  between  amphibole  and  pyroxene  —  especially  between  the  varieties 
hornblende  and  augite  —  it  is  very  desirable  for  the  trained  investigator  to  be  able  to 
discriminate  between  them,  since  the  determination  of  certain  rocks  depends  on  this. 
Moreover,  there  are  important  and  deep-seated  differences  between  them,  as  is  shown  by 
their  optical  and  microscopic  properties. 


DARK-COLOKED   MINERALS.  33 

with  a  hardness  equal  to  quartz.  Rarer  varieties  of  tourmaline 
are  brown,  green,  blue,  pink,  and  even  white.  The  mineral  con- 
tains boric  acid,  besides  silica,  alumina,  and  sundry  other  constit- 
uents in  various  proportions. 

The  last  of  the  dark  minerals  worthy  of  mention  is  hyper- 
sthene.  This  is  sometimes  a  rock  constituent  in  company  with 
labradorite.  It  occurs  in  masses  of  thin,  brittle  lamellae  of  a 
dark  brownish-green,  grayish-black,  greenish-black,  or  pinchbeck-- 
brown  color,  having  a  hardness  nearly  equal  to  orthoclase.  It 
has  about  the  same  constituents  as  amphibole. 

EXERCISES. 

Take  in  hand  a  rock  fragment  containing  a  dark  mineral,  and  state 
whether  the  mineral  is  scaly.  If  so,  are  the  leaves  elastic?  Are  they  brit- 
tle? What  is  their  color?  What  proportion  of  the  rock  do  they  form?  If 
not  scaly,  is  the  mineral  lamellar?  Is  it  fibrous?  What  is  its  color?  Is  it 
shining  or  dull  in  lustre?  If  the  scales  were  greenish,  what  mineral  would 
they  probably  be?  Would  they  then  be  elastic  or  not?  If  whitish,  what  min- 
eral would  they  probably  be?  Would  they  be  elastic  or  not?  Would  they  be 
harder  or  softer  than  mica?  If  the  scales  are  jet  black,  what  mica  have  we? 
What,  if  they  are  reddish?  What,  if  they  are  bronze-like?  What  points 
must  be  mentioned  in  describing  a  mineral?  Take  another  rock  specimen, 
and  describe  completely  the  most  abundant  mineral  in  it.  What  light- 
colored  minerals  do  you  see?  Pick  out  a  mineral  which  you  think  is  augite. 
What  particulars  lead  you  to  think  it  augite?  Pick  out  a  sample  of  horn- 
blende. What  differences  between  them  can  you  discern?  Which  has  most 
quartz  associated  with  it?  If  a  rock  contains  biotite,  is  the  other  dark 
mineral,  if  present,  likely  to  be  hornblende  or  augite?  Select  a  rock  contain- 
ing hydrornica.  Why  will  not  hydromica  effervesce?  What  may  hydromica 
be  mistaken  for?  Explain  why  the  surface  rock  often  contains  hydromica 
and  the  deep  quarry  rock  muscovite.  Did  you  ever  know  of  a  man  who  col- 
lected bowlders  containing  bronzy  mica,  thinking  this  mineral  to  be  gold? 
Search  for  specimens  of  tourmaline.  How  does  tourmaline  differ  from 
hornblende?  How  will  you  know  it  when  found? 


34  GEOLOGICAL   STUDIES. 


STUDY  VII. — Lime,  Magnesia,  and  Iron  Minerals. 

Among  important  rock  ingredients  two  yet  remain  to  be 
studied  which  belong  to  the  group  of  carbonates.  Some  of  the 
properties  of  carbonates  have  already  been  learned,  especially 
their  tendency  to  effervesce  when  strong  acids  are  applied  to 
them.  Chalk,  we  have  seen,  is  a  carbonate,  but  it  does  not  pre- 
sent any  crystalline  form  or  lustre.  It  is  simply  earthy,  and  con- 
sists of  a  mass  of  fine  particles  of  carbonate  of  lime  compacted 
together.  Marble  also  consists  of  a  mass  of  grains  and  particles 
somewhat  cemented;  but  marble  has  some  lustre.  There  are 
shining  faces.  In  fact,  a  close  inspection,  especially  with  a  magni- 
fier, shows  that  the  rock  is  composed  of  small  crystal  fragments. 
Some  marbles  are  sufficiently  coarse  to  show  the  crystalline  struc- 
ture very  distinctly. 

Now  we  frequently  find  these  crystals  sufficiently  large  to  be 
studied.  Let  us  seek  for  some  white  vein  running  through  an- 
other rock.  We  may  at  first  fall  upon  a  vein  of  white  quartz. 
The  tester  will  determine.  Suppose  we  have  found  a  white  min- 
eral or  fragment  large  enough  to  show  crystalline  form,  and  soft 
enough  to  be  easily  scratched.  Probably  this  is  calcite.  You 
cannot,  perhaps,  discover  the  complete  form;  but  if  you  scruti- 
nize closely,  you  will  notice  some  angles,  and  you  will  perceive, 
probably,  a  number  of  cracks  which  run  in  directions  parallel  with 
the  faces  revealed.  Perhaps  the  cut,  Fig.  18,  represents  part  of 
what  you  see.  Here  is  one  face  a,  bounded  by  another 
face  b,  forming  an  angle  along  the  line  m  n.  This  is 
not  a  right  angle,  but  is  greater  or  less.  You  see,  also, 
along  the  fractured  border  of  a  several  angular  sali- 
ences, which  are  bounded  on  one  side  by  planes  ex- 
actly parallel  with  b,  and  on  another  by  planes  parallel 
with  each  other,  and  in  fact  parallel  with  another  face 
of  the  broken  crystal.  The  directions  of  these  planes 
are  continued  in  cracks  passing  through  the  crystal. 
It  appears  that  the  crystal  is  made  up  of  many  small  crystals,  all 


LIME,    MAGNESIA,    AND    IRON   MINERALS. 


35 


FIG.  19.— CRYSTAL  OP 
CALCITE. 


having  the  same  shape.     If  we  could  get  one  of  these  crystals 
out,  it  would  present  the  form  shown  in  Fig.  19.     This  form  is  a 
rhombohedron.     If  you  take  a  cubical  box  and 
partly  crush  it  by  pressing  against  one  corner 
toward  the  corner  diagonally  opposite,  you  re- 
duce the  box  to  the  form  of  a  rhombohedron. 
Notice  particularly  the  difference  between  this 
and  common  forms  of  orthoclase. 

The  hardness  of  this  crystal  is  much  less  than  that  of  ortho- 
clase; and  this  furnishes  a  third  easy  means  of  separating  the 
two  minerals  —  effervescence,  want  of  right  angle,  and  lower  hard- 
ness. 

The  cracks  generally  apparent  indicate  cleavage  planes,  as 
Fig.  18  shows.  Every  fragment,  therefore,  presents  the  same 
angles  as  the  whole.  Calcite  is  sometimes  as  transparent  as 
glass,  and  then  known  as  Iceland  spar.  It  possesses  the  strik- 
ing property  of  double  refraction.  If  you  place  a  plate  of  Ice- 
land spar  on  a  printed  page,  you  see  every  letter  beneath  it 
double.  Calcite  is  more  commonly  almost  opaque.  Its  color  is 
nearly  always  white,  but  sometimes  we  find  it  yellowish,  delicate 
blue,  and  various  other  tints.  The  fundamental  rhombohedron  is 
also  frequently  modified,  and  the  forms  resulting  are  very  numer- 
ous. The  most  common,  however,  is  that  known  as  dog-tooth 
spar,  of  which  a  couple  of  large  crystals  are 
shown  in  Fig.  20. 

We  must  not  conclude  too  readily  that  a 
whitish  mineral  is  calcite,  even  when  soft 
enough  to  be  cut  with  a  knife.  Not  unfre- 
quently  we  encounter  crystals  having  the  lus- 
tre and  hardness  of  calcite,  but  with  curved 
faces  —  opposite  ones  being  convex  and  con- 
cave. Cold  dilute  acid  applied  to  these  does 
not  cause  effervescence,  even  after  they  are 
reduced  to  powder.  But  heat  applied  pro- 
duces it.  The  chemist  informs  MS  that  this 
mineral  is  composed  of  carbonate  of  lime, 


FIG.  20.— DOG-TOOTH 
SPAR. 


36  GEOLOGICAL   STUDIES. 

fifty-four  parts,  and  carbonate  of  magnesia,  forty-six  parts.  A 
mineral  having  this  composition  is  called  dolomite.  This  crystal 
with  curved  faces  is  a  variety  called  pearl  spar,  when  the  color 
is  white,  and  brown  spar  when  the  color  is  brown.  The  brown 
coloring  ingredient  is  iron.  So  manganese  or  cobalt  gives  a  red- 
dish dolomite. 

But  when  the  crystalline  faces  are  not  curved  it  is  difficult  to 
distinguish  dolomite  from  calcite  without  chemical  analysis.  We 
may  find  "veins"  of  coarse  dolomite  crystals  closely  resembling 
calcite  veins  in  color,  form,  and  hardness  of  the  mineral.  Our 
only  expedient  then  is  the  dilute  acid.  We  shall  see  that  dolo- 
mite is  a  mineral  almost  as  abundant  as  calcite,  and  hardly  less 
important. 

A  rock  ingredient  belonging  to  the  group  of  sulphates  is 
very  familiar.  It  is  soft  enough  to  be  crushed  between  the 
teeth.  Everyone  knows  gypsum  •  but  pure  crystallized  gypsum 
is  less  common.  It  occurs  in  distinct  crystals,  or  broad  leaves,  or 
plates,  sometimes  a  yard  across,  and  as  transparent  as  glass.  This 
variety  is  called  selenite.  One  of  the  crystal  plates  is  shown  in  Fig. 
21.  Gypsum  is  composed  of  sulphuric  acid  forty-six  and  one-half 

parts,  lime  thirty-two  and  one- 
half  parts,  and  water  twenty- 
one  parts.     When  subjected  to 
heat  the  water  is  expelled,  and 
the  gypsum  is  said  to  be  "cal- 
cined."   When  ground  gypsum 
FIG.  21.-A  TBA^SPARENT  CRYSTAL  OF          jg  calcined  it  constitutes  «  plas- 
ter  of    Paris  "  —  so   called   be- 
cause the  quarries  at  Montmartre,  Paris,  supplied  gypsum  for  cal- 
cination and  use  in  the  city.     The  Paris  gypsum,  however,  con- 
tained also  carbonate  of  lime.     When  calcined  gypsum  is  exposed 
to  water  it   reunites  with   a  certain   amount   of  water,  and  re- 
sumes a  high  degree  of  hardness.     In  other  words,  it  "sets."     It 
is,  therefore,  valuable  for  many  purposes. 

There  are  three  principal  ores  of  iron  which  in  some  regions 
exist  to  a  rock-making  extent.  Haematite  is  simply  an  oxide  of 


LIME,    MAGNESIA,    AND   IRON    MINERALS.  37 

iron,  composed  of  two  equivalents  (or  atoms)  of  iron  and  three 
of  oxygen.  Taking  the  mineral  by  weight,  one  hundred  parts  of 
haematite  contain  thirty  of  oxygen  and  seventy  of  iron.  This 
mineral  is  well  known  as  iron  rust.  In  nature  it  is  often  beauti- 
fully crystallized,  and  occurs  also  in  granular  and  stalactitic 
shapes,  and  in  lamina?,  either  thick  or  thin.  The  crystals  have  a 
metallic  lustre,  and  sometimes  are  truly  splendent.  Their  color 
is  steel  gray,  or  iron  black,  but  scales  thin  enough  to  transmit 
light  are  blood  red.  When  the  surface  is  shining  and  mirror- 
like,  the  mineral  is  called  "specular"  ore.  Haematite  sometimes 
occurs  in  thin  micaceous  scales,  and  frequently  in  compact  fibrous 
masses.  When  earthy,  it  becomes  red  chalk  and  red  ochre. 
Haematite  sometimes  attracts  the  magnetic  needle.  A  neat  way 
of  distinguishing  haematite  in  any  of  its  varieties  is  by  the  red 
color  of  its  powder  (called  streak).  Powdered  haematite  is,  there- 
fore, red,  and  is  much  used  as  a  red  paint. 

Limonite  is  simply  haematite  which  has  united  with  water. 
It  contains  sesquioxide  of  iron,  eighty-six  parts,  and  water,  four- 
teen parts,  in  one  hundred.  The  eighty-six  parts  of  the  ses- 
quioxide contain  twenty-six  parts  of  oxygen  and  sixty  parts  of 
iron.  We  find  limonite  commonly  in  stalactitic  or  botryoidal 
forms  —  the  latter  like  bunches  of  grapes  —  and  having  a  fibrous 
structure.  These  forms  often  possess  a  nearly  black,  glaze-like 
exterior.  In  the  mines  at  Salisbury,  Conn.,  Amenia,  N.  Y., 
and  in  many  other  localities,  the  cavities  of  the  rocks  often 
contain  groups  of  brilliant  black,  icicle-like  columns  of  limonite 
depending  from  the  roof  or  reaching  quite  to  the  floor  of  the 
cavity.  In  other  situations  this  ore  is  earthy,  and  constitutes 
ordinary  yellow  ochre.  This  is  the  iron  deposit  of  bogs,  where  it 
forms  bog  iron  ore,  of  which  we  have  before  spoken  (page  11). 
Limonite  is  easily  distinguished  by  its  yellow  or  yellowish-brown 
streak. 

Magnetite,  the  third  important  ore  of  iron,  is  known  by  its 
black  streak.  It  is  a  mixture  of  the  two  principal  oxides  of 
iron  —  protoxide  (or  one  of  oxygen  and  one  of  iron),  and  ses- 
quioxide (or  three  of  oxygen  and  two  of  iron).  The  amount  of 


38  GEOLOGICAL   STUDIES. 

oxygen  in  one  hundred  parts  by  weight  is  twenty-eight  parts, 
and    the    amount    of    iron    seventy-two.     This    ore, 
therefore,  contains  more  iron  per  ton  than  either  of 
the  others.     It  tends   to  crystallize   in    black    octa- 
hedrons, or  eight-sided  forms  like  Fig.  22,  which  are 
sometimes  found  scattered  through  crystalline  rocks. 
OCTAHEDRAL     Magnetite  is  so  named  because  it  strongly  attracts 
CRYSTAL  OP     the    magnetic    needle.      Occasional    pieces   possess, 
lTE'     also,  the  polarity  of  the  magnetic  needle,  and  these 
are   known  as  loadstone  or  lodestone.     There  are  several  other 
ores  of  iron  of  less  importance  than  these. 

W^e  ought  to  make  mention  of  a  few  additional  minerals 
which  sometimes  give  a  qualifying  character  to  rocks,  even  if 
they  are  not  constitutive,  like  the  others  named.  Pyrite  or 
pyrites  is  bronze  yellow,  hard  as  quartz,  and  occurs  in  cubes  and 
octahedrons.  It  is  composed  of  sulphur  and  iron.  Epidote  is 
mostly  a  pale  yellowish-green  mineral,  as  hard  as  quartz,  com- 
posed of  silica,  alumina,  lime,  and  iron.  It  is  known  principally 
in  a  massive  or  rock  condition,  as  a  constituent  of  crystalline 
rocks.  The  crystals  are  generally  elongated,  sometimes  needle- 
shaped  or  fibrous.  Garnet  is  a  generic  name  of  minerals  con- 
sisting of  silica  and  various  bases.  The  garnets  present  a  great 
range  of  colors,  but  the  common  garnet  is  a  deep  wine-red.  It 
is  an  iron-alumina  garnet;  when  transparent,  "precious  garnet." 
It  is  easily  recognized  by  its  twelve-sided  or  twenty  four-sided 
form.  Emery  is  an  impure  corundum.  The  latter  exceeds  quartz 
in  hardness,  and  consists  almost  wholly  of  alumina.  All  these 
minerals  may  be  found  in  common  bowlders,  and  the  student 
must  not  cease  to  search  until  he  finds  them. 

EXERCISES. 

What  is  the  nature  of  the  rusty  deposit  from  some  spring  waters?  What 
is  the  nature  of  the  white  deposit?  Suppose  haematite  combines  with  water, 
what  does  it  become?  If  limonite  loses  its  water,  what  does  it  become?  How 
many  pounds  of  iron  in  2,000  pounds  of  limonite?  How  many  in  2,000 
pounds  of  haematite?  How  many  in  2,000  pounds  of  magnetite?  How  many 


REVIEW   OF  THE   IMPORTANT   MINERALS.  39 

pounds  of  lime  in  2,000  pounds  of  calcite?  What  use  has  calcite  in  agricul- 
ture? Which  is  most  suitable  to  the  soil,  calcite  or  quicklime?  What  is  the 
difference  between  farm  plaster  and  plaster  of  Paris?  If  a  supposed  calcite  does 
not  effervesce  with  cold  acid,  what  may  be  concluded  as  to  its  composition? 
How  may  calcite  be  easily  distinguished  from  gypsum?  Name  all  the  white 
minerals  thus  far  described.  Which  is  hardest?  Which  softest?  Which 
next  to  hardest?  Show  a  specimen  of  calcite.  Show  some  other  minerals 
and  name  them.  How  can  you  distinguish  mica  from  micaceous  haematite? 
In  a  mass  of  iron  ore  kept  constantly  wet,  which  will  we  have,  haematite, 
limonite,  or  magnetite?  State  where  you  have  seen  any  of  these  ores.  Which 
ore  was  it?  How  do  you  know?  What  are  the  uses  of  emery?  What  is  an 
emery  wheel?  Have  you  found  calcite  in  a  rock  abounding  in  quartz?  If 
so,  was  the  calcite  generally  distributed  or  in  a  layer?  Was  it  fine-grained 
calcite  or  coarsely  crystalline?  Have  you  found  calcite  in  company  with 
biotite?  In  what  sort  of  rock  did  you  find  octahedrons  of  magnetite?  Show 
three  specimens  giving  the  three  streaks  of  the  principal  iron  ores.  Why  is 
hornblende  darker  than  calcite?  Why  is  it  heavier  than  calcite?  What 
minerals  have  you  now  in  your  collection? 


STUDY   VIII.— He-view  of  the  Important  Minerals. 

Of  the  thirty-five  or  forty  species  of  minerals  briefly  noticed, 
the  following  are  the  most  important  in  the  study  of  rocks: 
Quartz,  orthoclase,  plagioclase,  muscovite,  biotite,  hydromica, 
talc,  hornblende,  augite,  calcite,  and  dolomite.  The  student  who 
can  discriminate  these  under  their  various  aspects,  and  especially 
in  rocks  not  coarse-grained,  has  accomplished  much.  The  re- 
maining species,  nevertheless,  are  liable  to  be  met,  and  many  of 
them  constitute  important  ingredients  in  certain  rocks  not  gener- 
ally distributed.  This  will  appear  when  we  come  to  the  study  of 
rocks. 

We  have  prepared,  for  the  convenience  of  the  student,  a 
tabular  exhibit  of  the  chemical  composition  of  these  minerals, 
and  have  added  in  the  last  column  figures  expressive  of  the  hard- 
ness of  each.  The  meaning  of  these  figures  is  understood  by 
reference  to  certain  standards  of  hardness  as  indicated  on  page  42. 

A  few  species  are  mentioned  in  the  table  for  the  first  time. 


40 


GEOLOGICAL   STUDIES. 


TABLE  OF  COMPOSITION  OF 


MINERALS. 

OXYGEN. 

SILICA. 

ALUMINA. 

OXIDES 
OF  IRON. 

POTASH. 

SODA. 

Binary  Compounds. 

Suartz  
sematite 

53.33 
30 
25 
W.Q 

.   .   .. 

Magnetite  
Menaccanite 

Franklinite 

17 

"l2" 
9 
4 

Pyrite 

Halite  ("salt") 

Silicates. 

f  Orthoclase 

gl« 
68  ^jg 

i  'S 
G2)< 

53  |  o 

43  j| 
46.5 
47 

36 
40 

48 

18 
20 

24 

30 

37 
34.4 
33 

16 
15 
25 

'»" 

,.     Albite  i    ^ 
gi!  Oligoclase  -5 

s  1                    }•  s 

5     Lahradorite     ...      §> 
**<                                     j   -2 
L  Anorthite  J  ^ 
Kaolinite    





"i"" 

20 
5 
9 

'io' 

8 

7 
9 

'"2" 
3" 

f  Muscovite 

v  j  Biotite 

^     Phlogopite 



L  Lepidolite  

Talc 

63 

e5 

44 
31 

27 
50 

59 

57 

48 

54 

53 
52 
37 
38 
35 

Pyrophyllite 

Serpentine  

•  f  Ripiclolite         ...     . 

3 

4 

26 

8 

2 

5 

6 

9 
22 
12 
13 

28 

17 

19 
10 

'"2" 

|J 

I  1 

t>  tProchlorite 

«  f  Hornblende 

"5 

A 

<  -i  Tremolite  .  . 

"^  [  Actinolite 

•  f  Aueite 

7 

2 
8 

85 
22 

7 

|  -\  Sahlite  . 

^  IDiallage  
Hypersthene  
Tourmaline  (black) 





2 

Epidote 

Garnet 

Carbonates. 

Calcite 

CARBON- 
IC ACID. 
44 

47  83 

Magnesite  

52  A 
37.9 

Siderite  
Sulphate. 
Gypsum  

62.1 

REVIEW    OF   THE    IMPORTANT   MINERALS. 
THE  COMMON  MINERALS. 


41 


MAG- 
NESIA. 

IRON. 

WATER. 

OTHER  CONSTITUENTS. 

HARD- 
NESS. 

Silicon  46  67  

7 

70 

5  5-6 

60 

15 

555 

72.4 

Protox.   Iron  31.03-f  Sesquiox.  Iron  68.97. 
Often  with  Titanium  
Approximately,  Perox.  and  Protox.  Iron  54 
+  Oxide  Titanium  43  
Haematite  66  -f-  Sesquiox.  Mangan.  14  -j-  Pro- 

5.5-6.5 
5-6 

tox.  Zinc  20  

5  5_6  5 

46  5 

Sulphur  53 

6-6  5 

Sodium  39.  3  +  chlorine  60.7  

2  5 

LIME 

5  7 

6-7 

5 

6-7 

13 

6 

20 

6-7 

24  1 

1-2.5 

1 



Most  actual  examples  1-5  p.c.  water,  by  al- 
teration        

2-2.5 

17 

2.5-3 

28 

253 

Lithia  4  +  Fluorine  5            

2  5-4 

5-10 

1-2 

32 

5 

1-1.5 

1 

5 

1-2 

43 

12 

2.5-4 

33 

13 

2-2.5 

16 

U 

1-2 

15 

12 

Iron  is  mostly  Protoxide,  and  ranges  to  20 

5-6 

25 

13 

The  Iron  is  a  Protoxide                       

5-6.5 

13  4 

20 

The  Iron  is  a  Protoxide                  .  .          ... 

5-fi 

15 

21 

15 

23 

16 

19 

22 

2 

5-6 

2 

Fluorine  2  -f-  Boron  8         

7-7.5 

22 

28 

56 

2 

Manganese  oxide  0-5  
This  is  the  common  Lime-Iron  Garnet  

6-7 
6.5-7.5 

2.5-3.5 

21.73 

29.44 



Carbonate   Lime    54.35  +  Carb.    Magnesia 
45  65 

3  5-4 

47  6 

3.5-4.5 

....   .  . 

3.5-4.5 

09   c 

20  9 

1.5-2 

42  GEOLOGICAL   STUDIES. 


SCALE    OF   HARDNESS. 

1.  Talc,        t  Scratched  with  the  finger  nail. 

2.  Gypsum,  ) 

3.  Calcite,  i  Easily  cut  with  a  knife. 

4.  Fluorite  (Fluor  Spar),  ) 

5.  Apatite,  Cut  with  difficulty. 

6.  Orthoclase,  Barely  scratched  by  steel. 

7.  Quartz,  1 

8.  Topaz  or  Beryl,    ^  Not  scratched  by  steel. 

9.  Corundum, 
10.   Diamond, 

The  "Table  for  Determinations"  must  not  be  regarded  as  an 
infallible  guide,  but  it  will  probably  be  an  aid  to  the  student.  A 
great  deal  of  exercise  should  be  had  on  it. 

TABLE  FOR  DETERMINATION  OF  MINERALS. 

Hardness  6.5  to  7  or  over. 
Lustre  vitreous. 
Color  black ;  sometimes  brown,  green,  blue,  pink  or  white ; 

often  in  prisms  with  curved,  striated  or  fluted  sides,  Tourmaline. 
Color  yellowish-green,  Epidote. 

Color  deep  red,  crystalline  form  conspicuous,  12-24-sided,  Garnet. 

Color  whitish,    dusky,    reddish;    transparent  when  pure; 

crystalline  faces  not  shown  on  fracture. 

No  double  refraction ;  crystal,  a  6-sided  prism,  Quartz. 

Double  refraction  strong  (when  transparent) ;  crystal  oc- 
tahedral or  cubical,  Andalusite. 
Lustre  metallic ;  color  brass  yellow,  Pyrite. 
Hardness  4.5  to  6. 
Streak  brownish  yellow;  lustre  silky;  often  stalactitic  or 

botryoidal,  Limonite. 

Streak  red ;  often  lamellar,  columnar  or  granular,  Hcematite. 

Streak  dark  reddish-brown ;  acts  slightly  on  the  magnet,         Franklinite. 
Streak  submetallic;  powder  black  to  brownish  red,  Menaccanite. 

Streak  black,  lustre  metallic ;  crystals  often  octahedral,  Magnetite. 

Streak  light. 

Streak  white ;  color  mostly  light,   ranging  through  white, 
gray,  red,  brown  and  green ;  lustre  pearly  or  vitreous- 
pearly  ;  texture  not  fibrous  (FELDSPAR). 
With  right-angled  crystallization ;  no  surface  striations ; 

colors  mostly  white,  creamy  and  pale  red,  Orthoclase. 


REVIEW   OF  THE   IMPORTANT   MINERALS. 


43 


No  exact  right  angle;  striations  often  present;  colors 
bluish,  grayish,  greenish,  dusky  or  white,  sometimes 
glassy  transparent,  Plagioclase. 

Streak  pale  greenish. 
Color  black  or  greenish  black;  texture  often  fibrous; 

having  no  prismatic  right  angle  (AMPHIBOLE).  Hornblende. 

Color  green,  greenish  or  greenish-black ;  often  white  if 

fibrous. 
Texture  seldom  fibrous;  having  a  prismatic  angle  of 

nearly  90°  (PYROXENE),  Augite. 

Texture  of  radiating,  prismatic,  greenish  fibres,  Actinolite. 

Texture  of  fine,  parallel,  whitish  fibres  or  blades,  Tremolite. 

Streak  grayish  or  brownish-gray;    color  dark  brownish- 
green,  grayish-black,    greenish-black;    lustre   some- 
times a  little  metalloidal,  Hypersthene. 
Hardness  from  3  to  4. 

Effervescence  with  acids;  color  generally  nearly  white;  some- 
times transparent ;  lustre  vitreous  or  vitreous  pearly. 
Effervescence  with  cold  acid ;  faces  not  curved ;  often  trans- 
lucent or  transparent;  generally  distinctly  rhombo- 
hedral,  Calcite. 

Effervescence  only  with  hot  acid. 
Lustre  inclining  to  pearly;  color  often  brownish;  faces 

sometimes  curved,  Dolomite. 

Lustre  vitreous. 

Color  white,  yellow,  gray,  brown,  green,  Magnesite. 

Color  ash-gray  to  brown  or  red,  Siderite. 

No  effervescence  with  acids;  lustre  greasy,  waxy  or  earthy; 

color  greenish ;  occuring  only  massive,  Serpentine. 

Hardness  below  3;  no  effervescence  with  acids. 
Structure  distinctly  foliaceous. 
Folia  elastic  when  unweathered. 

Colors  from  black  to  greenish;  lustre  splendent,  Biotite. 

Colors  gray,   brown,    greenish,  violet,    yellowish,  olive- 
green  ;  often  transparent,  Muscovite. 
Colors   yellowish-brown   to  brownish,  often  with  copper 

reflections,  PJilogopite. 

Colors  grass-green  to  olive-green;  transparent  to  trans- 
lucent, Ripidolite. 
Folia  inelastic,  greenish,  reddish  or  black. 

Color  pink  or  pinkish,  Lepidolite. 

Color  apple-green  to  whitish;  folia  flexible  but  inelastic ;  j  Talc. 

feel  greasy,  <  Pyrophyllite. 


44  GEOLOGICAL   STUDIES. 

Color  deep  green  (CHLORITE). 

Hanging  from  grass-green  to  olive-green ;  folia  some- 
what elastic;  transparent  to  translucent,  Ripidolite. 
Ranging  from  grass-green  to  blackish-green ;  translu- 
cent to  opaque,                                                                 Prochlorite. 
Color  black;    folia  flexible;   feel  greasy;  streak  black; 

lustre  metallic,  Graphite. 

Structure  indistinctly  foliaceous  or  compact ;  green  or  green- 
ish; lustre  earthy,  Hydromica. 
Structure  not  foliaceous ;  sometimes  lamellar. 

Color  light;  lustre  vitreous  or  silky ;  crystals  transparent,          Gypsum. 
Color  black;  blackens  white  paper;  in  granular  masses,  Graphite. 


STUDY  IX.—  Quartzose  Rocks. 

We  return  now  to  the  field  and  resume  our  intercourse  with 
the  bowlders.  We  should  be  prepared  to  study  them  now  as 
rock  specimens.  Any  accessible  rocks  "in  place  "  —  bed  rocks  — 
will  be  quite  as  suitable,  and  should  be  especially  studied;  but 
taking  our  country  at  large,  not  one  tenth  of  our  students  could 
depend  on  finding  a  supply  of  rock  specimens  without  recourse  to 
bowlders.  These  are  almost  everywhere  throughout  our  northern 
states.  On  the  prairies  and  in  the  southern  states  where  bowlders 
do  not  abound,  they  should  be  obtained  from  some  bowlder-cov- 
ered region.  They  should  be  had  in  large  supply.  Regions 
abounding  in  bowlders  are  even  better  situated  for  lithological 
studies  than  other  regions,  since  the  number  of  species  to  be  had 
on  a  square  mile  is  much  greater  than  would  be  supplied  within 
an  equal  area  by  rocks  in  place. 

You  have  noticed  that  all  the  rocks  which  thus  far  have  been 
in  our  hands  for  mineral  study  have  been  hard  and  made  up  of 
grains  which  are  either  crystals  or  fragments  of  crystals.  They 
are  therefore  known  as  crystalline  rocks.  On  the  contrary,  the 
bed  rocks  in  most  portions  of  the  country  are  not  so  hard  and 
crystalline.  They  consist  of  limestones,  sandstones  and  shales, 
having  mostly  a  dull  lustre,  often  containing  fossils;  and  if  the 
constituents  are  sufficiently  coarse  to  be  detected  with  the  mag- 


QUARTZOSE   ROCKS.  45 

nifier,  they  are  seen  to  be  rounded  as  if  they  had  themselves,  at 
some  time,  been  rolled  about  like  bowlders.  Many  limestones, 
however,  are  exceptions  to  this  statement,  some  of  them,  and 
most  marbles,  being  decidedly  crystalline.  You  have  remarked 
then  two  series  of  rocks,  the  crystalline  and  the  fragmental; 
and  you  already  know  that  nearly  all  our  bowlders  belong  to  the 
crystalline  series.  Of  the  crystalline  rocks  you  have  already  no- 
ticed many  sorts  or  species,  and  you  will  find  them  very  much 
more  diversified  than  the  fragmental. 

Probably  the  first  bowlder  which  we  attempt  to  study  will  be 
a  quartzite  —  a  rock  composed  wholly  of  quartz,  or  nearly  so, 
and  either  massive  or  thick-bedded.  Glancing  over  the  field,  you 
will  probably  notice  many  white  or  very  light-colored  bowlders. 
Inspect  one  of  them  closely.  Test  it  for  hardness.  You  make 
no  scratch.  Examine  its  structure.  Can  you  trace  the  outlines 
of  its  constituent  fragments  or  grains?  If  you  can  do  this  easily, 
the  quartzite  is  granular.  But  if  you  find  the  constituent  grains 
closely  pressed  together,  so  that  they  seem  to  have  indented  each 
other  and  blended  together,  the  quartzite  is  vitreous.  Sometimes 
it  is  so  vitreous  as  to  almost  constitute  something  like  a  mass  of 
opaque  glass.  On  the  other  extreme,  the  grains  are  sometimes 
so  little  adherent  that  the  rock  crumbles,  and  is  then  &  friable 
quartzite.  All  this  you  can  easily  demonstrate  in  the  field. 
Otherwise,  the  different  sorts  of  specimens  can  be  collected  and 
brought  before  the  class,  and  placed  in  your  hands. 

There  are  several  other  varieties  of  quartzites.  They  may  be 
fine  or  coarse.  When  they  contain  pebbles  they  are  quartzose 
conglomerates.  Some  are  composed  chiefly  of  white  porcelain- 
like  quartz;  others,  of  a  more  glassy  quartz.  Some  have  grains 
or  pebbles  of  jasper — red  jasper  being  quite  common.  These 
are  jaspery.  There  may  be  present  sparsely  scattered  crystalline 
fragments  of  mica,  hornblende,  talc,  chlorite,  or  other  minerals 
which  give  a  qualified  character  to  the  quartzite.  It  is  then 
micaceous,  hornblendic,  talcose,  or  chloritic.  Quite  often  the 
peculiar  straight,  long,  black  crystals  of  tourmaline  are  seen. 
With  a  little  patience  you  may  collect  twenty  or  more  varieties 
of  quartzite. 


46  GEOLOGICAL   STUDIES. 

But  we  have  also  fragmented  quartzose  rocks.  The  common 
sandstone  seen  in  the  bluff  or  used  in  some  of  our  buildings  is 
composed  merely  or  mostly  of  grains  of  quartz.  But  when  you 
inspect  the  rock,  the  shining  lustre  of  the  quartzite  is  wanting, 
and  the  grains  are  not  so  closely  compacted  together.  The 
sandstone,  therefore,  is  more  easily  broken;  and  friable  kinds  are 
of  more  frequent  occurrence.  Moreover,  you  will  notice  in  every 
sandstone  the  presence  of  foreign  particles,  sometimes  of  an 
earthy  character  and  sometimes  of  other  minerals  not  quartzose. 
Among  fragmental  quartzose  rocks  there  are  also  conglomerates 
and  grits  and  materials  of  various  colors,  making  the  general  tint 
of  the  rock  gray,  bluish,  reddish,  purplish,  or  even  nearly  white. 
The  character  of  the  sandstone  may  also  be  qualified  by  the 
presence  of  foreign  ingredients  like  mica,  clay,  calcite,  iron-rust, 
bitumen,  petroleum,  or  coaly  matters.  It  is  then  micaceous, 
argillaceous,  calcareous,  ferruginous,  bituminous,  petroliferous, 
or  carbonaceous. 

Most  of  the  quartzites  show  little  evidence  of  stratification  or 
arrangement  in  layers  or  "beds."  Others  are  thick-bedded,  and 
still  others  are  thin-bedded,  and  present  a  finer  and  generally 
more  homogeneous  texture.  These  are  silicious  schists.  By 
the  addition  of  mica,  hornblende,  or  other  minerals,  they  become 
schists  of  other  sorts,  as  we  shall  see.  When  the  bedded  quartz- 
ites contain  argillaceous  matter,  and  are  extremely  fine  and  uni- 
form, they  constitute  novaculite.  When  they  are  reddened  by 
an  abundance  of  haematite,  they  form  a  jasper  schist.  The 
jaspery  materials  are  generally  arrang-ed  in  ribbon-like  bands 
alternating  with  materials  more  hagmatitic  or  more  purely  sili- 
cious. These  bands  are  often  so  folded  and  contorted  as  to  con- 
stitute a  curious  and  instructive  study. 

The  materials  of  quartzose  rocks  sometimes  occur  quite  un- 
cemented.  Indeed,  all  beds  of  sand  are  such,  and  illustrate  what 
is  supposed  to  have  been  the  remote  condition  of  most  quartzose 
rocks.  How  the  sand,  in  the  course  of  time,  has  become  so 
consolidated  is  not  fully  understood.  Among  some  fragmental 
rocks,  however,  we  can  detect  some  kind  of  cement.  Oxide  of 


QUARTZOSE    ROCKS.  47 

iron  sometimes  serves  as  such  cement,  and  this  imparts  a  reddish 
or  yellowish  color  to  the  rock.  Carbonate  of  lime  is  a  common 
cement,  and  in  such  cases  can  be  detected  with  the  naked  eye  or 
the  lens  as  a  whitish  filling  of  the  interstices.  Its  presence,  also, 
is  denoted  by  a  slight  effervescence  with  acids.  Some  sandstones 
are  so  highly  calcareous  that  on  breaking  the  rock  sparry  reflect- 
ing faces  are  visible  running  through  it  for  short  distances. 
These  are  faces  of  the  rhombohedral  form  under  which  the  car- 
bonate of  lime  has  crystallized. 

Many  of  you  have  noticed,  scattered  over  the  fields,  flattened 
rounded  stones  of  dark  reddish  color  and  considerable  weight, 
apparently  containing  iron,  but  also  with  more  or  less  fine  sand 
disseminated  through  them.  As  found  in  the  soil,  they  are 
generally  composed  of  concentric  layers,  one  within  the  other. 
The  outer  layers  are  distinctly  reddish,  and  not  very  hard,  but 
there  is  generally  a  central  nucleus  which  is  grayish-black,  com- 
pact, and  hard.  Quite  often  the  outer,  softer  layers  are  detached 
from  the  inner  mass;  and  this  often  takes  place  before  the  stone  is 
broken.  The  nucleus  can  then  be  heard  rattling  within,  when 
the  stone  is  shaken.  These  stones  are  the  subjects  of  much 
curiosity  and  conjecture  among  those  ignorant  of  geology.  They 
are  often  called  "iron-stones,"  "kidney  iron-stones,"  or  when 
clayey,  "clay  iron-stones,"  and  with  a  little  more  correctness, 
"iron  nodules"  or  "iron  concretions."  Now,  the  chemist  as- 
certains for  us  that  they  are  composed  chiefly  of  carbonate  of 
iron,  and  are,  therefore,  impure  siderite.  Our  own  inspection 
reveals  a  concentric  structure,  showing  that  they  are  ferruginous 
concretions.  That  is,  the  iron  matter  began  at  first  to  collect 
around  a  centre  in  some  sand  or  clay  rock,  then  successive  layers 
collected  around  the  first  ones,  so  that  the  whole  concretion  is 
composed  of  a  succession  of  concentric  layers.  It  may  be  sup- 
posed the  carbonate  of  iron  moved  through  the  rock  in  a  state  of 
solution.  Arriving  at  its  place,  the  carbonate  was  precipitated. 
When,  at  some  later  time,  the  nodule  was  left  on  the  surface, 
exposed  to  the  air,  the  iron  on  the  exposed  exterior  united  with 
more  oxygen  and  became  a  peroxide,  causing  the  carbonic  acid  to 


48  GEOLOGICAL   STUDIES. 

escape.  As  far  as  this  action  penetrated,  a  rusty  shell  was 
formed.  Deeper  within,  the  original  condition  remained.  This 
is  the  state  of  partial  change  in  which  we  find  it.  Now,  if  we 
reason  correctly,  the  process  of  oxidation  is  continuing,  and  in 
the  course  of  time  will  penetrate  to  the  centre.  Also,  as  the 
oxidation  has  penetrated  only  a  certain  distance,  our  thoughts  go 
back  to  the  commencement  of  the  process.  It  had  a  beginning, 
and  that  was  not  very  far  back  in  time;  for  if  it  were,  the 
oxidation  would  have  reached  to  the  centre  before  our  day. 
Now,  if  we  could  ascertain  how  many  years  have  been  required 
for  the  oxidation  to  penetrate  one-sixteenth  of  an  inch,  we  could 
easily  calculate  how  long  since  the  work  began,  if  we  might 
assume  that  the  progress  of  it  has  been  uniform.  That  is,  the 
calculation  would  show  how  long  a  time  has  elapsed  since  those 
geologic  events  took  place  which  left  the  nodule  exposed  to  the 
peroxidizing  action. 

The  process  of  concretion  is  noticed  in  other  kinds  of  min- 
erals, as  we  shall  see.  In  ferruginous  sandstone  quarries  we  can 

^^^  sometimes  observe  it  going  on. 

'f''''-'.".i!^-  .,••,!,.  »"'^ -..  ......     A  freshly  exposed  surface  of  the 

i  *7l'«-T  'i    ' '  *•*•'•''/?'?•?£-'  <•'  ',-'.V'  '<:  -"'.':  •••'*-  ''.'''."; 

'.'•>''.V'.>.-.^J;^f^zJi. .•'^•.•.•.\V:3'.-'-1'-'?V; A  •/-,.  •'.     formation    may    exhibit    a   rude 

concretionary   structure   extend- 
ing  across   two   or  more   strata, 
as  represented  in  Fig.   23.     As 
the  concretionary  lines  cross  the 
FIG.  23,-CoNCRETioNARY  STRUCTURE      lines   of    stratification,   they  are 
CROSSING  SANDSTONE  STRATA.  - 

more    recent    than    they.       I  he 

arrangement  of  the  material  must,  therefore,  have  taken  place  in 
the  rock.  In  certain  sandstones  some  of  the  iron  bands  become 
extremely  solid. 

Quartzose  rocks  undergo  less  change  than  any  others  on  ex- 
posure to  the  weather.  They  make,  therefore,  extremely  durable 
building  stones.  Some  of  the  sandstones,  like  the  Ohio  and  Nova 
Scotia  freestones,  and  the  Connecticut  valley  "brown  stones," 
are  very  highly  esteemed.  Even  the  flinty,  quartzite  bowlders, 
in  regions  where  other  good  building  stones  are  wanting,  are 


QUARTZOSE    ROCKS.  49 

sometimes  broken  up  and  dressed  into  shape  for  use  with  other 
dressed  bowlders.  Much  sandstone  is  too  incoherent  for  building 
purposes,  and  other  sandstones  after  use  develop  rusty  stains, 
through  the  peroxidation  of  the  iron  which  they  contain.  The 
disintegration  of  friable  sandstones  has  often  resulted  in  extensive 
beds  of  sand,  which  are  used,  as  well  as  the  drift  sand,  in  the 
preparation  of  mortar.  When  the  sand  is  white  and  quite  free 
from  iron,  it  is  employed  in  glass  making.  Grindstones  and 
whetstones  are  made  from  fine  and  even-grained  sandstones. 
Scythe  stones  are  generally  made  from  a  fine-grained  mica  schist, 
of  which  we  shall  learn  hereafter.  Many  hones  are  formed  of 
fine  homogeneous  silicious  schist.  One  well  known  sort  comes 
from  Nova  Scotia;  but  the  favorite  hones  are  "Arkansas  stones." 
Others  are  made  from  novaculite.  These  are  some  of  the  common 
uses  of  quartzose  rocks. 

EXERCISES. 

Pick  out  from  this  collection  of  specimens  all  the  quartzites.  Select  the 
vitreous  quartzites.  Separate  the  granular  quartzites.  Indicate  those  some- 
what intermediate  in  structure.  Point  out  a  quartzose  vein.  How  does  a 
sandstone  differ  from  a  quartzite?  Show  a  quartzite  having  two  or  more 
varieties  of  quartz.  Point  out  a  jaspery  quartzite.  One  with  tourmaline. 
One  with  mica  scales.  One  with  a  little  feldspar.  Show  a  stratified  quartz- 
ite. How  does  this  differ  from  a  sandstone?  Exhibit  a  ferruginous  sand- 
stone. What  is  its  color?  What  does  that  color  result  from?  Show  an 
argillaceous  sandstone.  Find  some  concretionary  structure.  What  are  the 
colors  in  it?  What  is  the  material?  Why  is  one  ferruginous  sandstone  yel- 
low and  another  red?  What  change  of  color  takes  place  when  the  yellow 
one  is  burned?  What  is  the  cause  of  the  change?  Why  are  quartzose  rocks 
used  for  sharpening  purposes?  What  is  sand  paper?  What  is  emery  paper? 
Which  is  most  efficient,  and  why?  What  is  a  razor  stone?  Indicate  some 
building  in  which  sandstone  is  used.  For  what  parts  is  it  used?  Whence 
was  it  obtained?  State  what  defect  is  liable  to  appear  in  a  sandstone  used  in 
building.  Why  do  defects  reveal  themselves  after  the  stone  is  built  in,  and 
not  previously?  What  are  flagstones?  Mention  a  locality  which  affords 
good  flagstones.  What  defects  sometimes  appear  in  flagstones  after  use? 
What  is  the  cause  of  stains?  Why  do  portions  scale  off?  Why  do  flag- 
stones sometimes  break  through  the  middle?  Do  the  cracks  generally  run 
with  the  walk,  or  across  the  walk?  What  does  this  indicate?  How  are  arti- 
ficial flagstones  made?  What  is  a  chalcedonic  quartzite?  A  tourmalinic 


50  GEOLOGICAL   STUDIES. 

quartzite  ?    Let  two  students  have  the  task  of  collecting  all  possible  varieties 
of  quartzose  rocks,  collecting  for  some  weeks,  as  opportunity  offers. 

STUDY  X. — Micaceous,  Amphibolic,  and  Pyroxenic  Rocks. 

I.     Micaceous  Rocks. 

No  bowlders  are  more  abundant  than  those  containing  mica. 
On  every  hand  its  glistening  scales  may  be  seen  reflecting  the 
sunlight.  It  exists  in  all  proportions  from  the  scattered  scales 
which  characterize  a  micaceous  sandstone  or  quartzite  to  such 
quantities  as  make  it  determinative  of  the  character  and  name  of 
the  rock.  When  a  quartzite  contains  as  much  as  twenty-five  per 
cent  of  mica,  it  forms  the  rock  known  as  greisen  (pronounced 
gri'sen). 

We  may  return  now  to  the  same  specimens  used  when  study- 
ing dark-colored  minerals.  Here,  besides  the  mica  apparent  in 
certain  of  them,  we  notice  one  or  more  light-colored  sorts.  Is 
either  of  them  quartz  ?  Test  its  hardness.  Is  either  of  them 
feldspar?  Remember,  you  determine  this,  first,  by  hardness 
inferior  to  quartz,  and  superior  to  calcite;  second,  by  its  some- 
what pearly  instead  of  glassy  lustre;  and  third,  by  its  reflecting 
cleavage  faces,  which  do  not  occur  in  quartz.  If  you  are  cer- 
tain we  have  in  this  rock  quartz,  feldspar,  and  mica,  each  in 
considerable  abundance,  and  no  other  mineral  in  much  abun- 
dance, then  the  rock  is  granite,  if  it  is  massive  or  unstratified; 
but  if  it  be  thick-bedded,  the  rock  is  gneiss  (pronounced  gnice). 
If  it  is  thin-bedded,  with  a  large  percentage  of  feldspar,  it  is  also 
gneiss;  but  generally,  when  thin-bedded,  the  percentage  of  feld- 
spar is  rather  small;  the  rock  is  composed  chiefly  of  mica  and 
quartz,  and  is  called  mica  schist.  In  all  these  rocks  the  mica 
may  be  of  any  species,  and  so  of  the  feldspar  also. 

The  proportions  of  these  constituents  of  granite  and  gneiss 
may  vary  to  a  great  extent,  and  in  this  the  general  complexion  of 
the  rock  may  vary.  We  have  very  light  granites  and  quite  dark 
granites.  Besides  this,  the  colors  of  the  quartz  may  vary,  as  well 
as  those  of  the  feldspar.  If  either  the  quartz  or  the  feldspar  is 


MICACEOUS,    AMPHIBOLIC,    AND    PYROXENIC    ROCKS.          51 

quite  red  and  is  abundant,  while  the  mica  is  subordinate,  then  we 
have  a  decidedly  reddish  granite.  The  rock  may  also  vary  in 
fineness.  Fine  granites  are  most  durable  for  building  stones. 
Sometimes  you  find  great  crystals  of  feldspar  or  great  flakes  of 
mica,  giving  you  the  constituents  of  granite,  but  scarcely  suffi- 
ciently mixed  to  form  a  proper  granite. 

Some  recent  lithologists  do  not  separate  granite  from  gneiss; 
and  it  is  certainly  difficult,  sometimes,  to  decide  from  a  hand 
specimen,  whether  the  rock  is  stratified  or  not.  We  can  only  say 
that  if  the  different  minerals  are  equally  distributed,  the  rock 
may  be  pronounced  massive;  but  if  the  mica  is  ranged  across  the 
stone  in  bands,  however  indistinct,  we  may  set  the  rock  down  as 
stratified.  But  these  bands  and  the  intervening  feldspar  or 
quartz  must  not  be  regarded  as  beds  or  strata.  They  are  only 
laminae.  They  may  be  of  any  thinness  without  making  a  thin- 
bedded  rock.  True  beds  are  marked  off  by  partings.  The  beds 
in  a  gneiss  may  be  one,  two,  or  eight  feet  thick,  each  marked  by 
thin  laminae. 

Now,  here  is  a  rock  —  a  very  common  one,  too  —  in  which  very 
little  mica  can  be  found.  It  is  simply  quartz  and  feldspar.  We 
shall  call  this  rock  granulite,  if  it  is  massive,  and  granulite  gneiss 
if  it  is  thick-bedded.  Some,  not  regarding  mica  a  necessary  con- 
stituent of  gneiss,  call  this  proper  gneiss;  and  then  as  a  difference 
of  composition  needs  to  be  indicated  some  way,  they  call  this 
"  binary  gneiss."  We  shall  use  terms  uniformly  as  first  explained. 
If  the  bedding  becomes  thin,  the  rock  becomes  a  granulite  schist. 
Then,  if  the  feldspar  fails,  the  rock  is  simply  a  quartzose  schist. 
We  study  these  granular  quartz-feldspar  rocks  here,  because  they 
sometimes  contain  a  little  mica,  and  are  always  associated  with 
micaceous  rocks,  and  behave  like  them. 

You  will  recall  that  altered  product  hydromica.  This  gives 
us  a  series  of  rocks  parallel  with  that  afforded  by  mica.  Hence 
we  have  hydromica  granite,  hydromica  gneiss  and  hydromica 
schist.  Some  hydromica  schists  are  very  fine-grained  and  homo- 
geneous, having  a  bluish-gray  color. 

Any  of  these  rocks  are  liable  to  contain  accessory  minerals. 


52  GEOLOGICAL   STUDIES. 

Garnets  very  often  occur  in  gneiss  and  mica  schist.     Other  fre- 
quent minerals  are  tourmaline,  epidote,  chlorite,  and  andalusite. 

II.     Amphibolic   and  Pyroxenic  Rocks. 

The  foregoing  are  the  rocks  resulting  in  case  the  dark  mineral 
in  our  hands  is  mica.  But  taking  another  specimen,  in  which  the 
dark  mineral  is  not  mica,  we  have  to  consider  whether  it  is  horn- 
blende or  augite.  It  is  probably  one  or  the  other,  if  the  mineral 
is  constitutive  —  that  is,  sufficiently  abundant  to  give  character 
to  the  rock.  Is  the  dark  mineral  hornblende  ?  Well,  if  we  have 
only  quartz  with  the  hornblende,  the  rock  is  a  hornblendic  quartz- 
ite,  if  massive  or  thick-bedded,  and  a  hornblende  schist,  if  thin- 
bedded  —  whether  a  little  feldspar  is  added  or  not.  But  if  the 
rock  is  almost  wholly  of  hornblende,  it  is  called  hornblende  rock 
or  amphibolite.  Sometimes  such  a  rock  is  extremely  fine-grained 
—  cryptocrystalline  —  and  it  is  then  one  of  the  varieties  of  aph- 
anite. 

If,  however,  we  have  quartz  and  feldspar  with  the  hornblende, 
the  rock  is  syenite,  if  massive  —  named  from  Syene  in  Egypt, 
where  the  same  species  of  rock  was  quarried  by  the  Egyptians 
centuries  ago.  As  in  the  micaceous  series,  the  rock,  if  thick- 
bedded,  is  gneissoid;  but,  as  it  has  not  the  composition  of  simple 
gneiss,  we  will  designate  it  syenitic  gneiss.  Similarly,  if  the 
rock  is  thin-bedded,  we  will  call  it  hornblende  schist.  If,  from 
syenite  the  quartz  disappears,  the  rock  becomes  hyposyenite  if 
the  feldspar  is  orthoclase. 

Many  writers  apply  the  name  granite  to  syenite  and  hypo- 
syenite;  and  some  use  the  single  term  gneiss  for  these  and  the 
true  gneiss.  If,  however,  rocks  are  to  be  distinguished  by  their 
mineral  composition,  and  terms  are  to  be  employed  to  express 
distinctions,  there  appears  no  good  reason  for  suppressing  the 
terms  "  syenite,"  "  syenitic  gneiss "  and  "  granite,"  from  the 
nomenclature  of  so-called  metamorphic  rocks,  or  those  in  which 
the  crystallization  is  a  secondary  result,  in  distinction  from  erup- 
tive rocks.  We  shall  employ  the  terms  uniformly  as  indicated 
above. 


MICACEOUS,   AMPHIBOLIC,    AND    PYROXENIC    ROCKS.  53 

You  must  have  remarked  the  great  resemblance  between 
granite  and  syenite,  especially  when  the  grains  of  the  black  min- 
eral are  very  small;  more  especially  if  it  is  black  mica  which  has 
begun  to  lose  its  lustre  by  absorption  of  water.  In  your  visit  to 
the  stone-cutter,  you  found  him  calling  them  all  "  granite,"  but 
many  reputed  granites  are  more  accurately  syenites.  "  Scotch 
granite  "  is  a  syenite  containing  much  red  orthoclase.  Most  of 
the  so-called  granites,  from  Maine  to  Massachusetts,  are  syenites. 
The  Quincy  granite  is  a  syenite.  The  capitol  at  Albany  is 
chiefly  syenite.  In  fact  the  great  masses  of  crystalline  granitoid 
rocks  in  the  northwest,  as  well  as  New  England,  are  chiefly  syen- 
ites instead  of  granites.  But  good  granites  occur  among  our 
bowlders,  and  we  shall  certainly  secure  specimens.  The  "  Obe- 
lisk," in  New  York,  is  a  micaceous  syenite  rich  in  feldspar  and 
with  relatively  large  crystals  of  hornblende  greatly  subordinate 
to  the  mica.  The  Mormon  Temple,  at  Salt  Lake  City,  is  the 
same  but  finer. 

But  what  are  these  granite-like  rocks  which  contain  no  quartz? 
We  have  handled  many  a  specimen.  Here  is  one  composed  of 
hornblende  and  orthoclase.  Some  call  it  simply  "granite"; 
some  "syenite";  some  " quartzless  syenite";  others,  hyposyen- 
ite.  We  shall  avoid  confusion  and  promote  convenience  by 
using  the  latter  name.  But  here  is  another  rock  in  which  the 
feldspar  is  striated  —  it  is  triclinic,  or  plagioclase.  Hornblende 
and  a  plagioclase  have  generally  been  called  diorite,  if  the  rock 
is  granite-like  in  texture.  But  we  have  to  be  a  little  more 
precise.  There  are  several  species  of  plagioclase.  There  is 
one  group  of  them  which  is  acidic,  like  albite  and  oligoclase, 
having  a  large  percentage  of  silica  (see  Table);  and  another 
group  which  is  basic,  having  less  silica.  Now  we  had  better 
restrict  the  term  diorite  to  mixtures  of  hornblende  and  an 
acidic  plagioclase.  Then  mixtures  of  hornblende  and  a  basic 
plagioclase,  like  labradorite  and  anorthite,  will  be  called  norite 
(called  also  gabbro  by  some,  but  this  name  is  used  in  various 
senses).  Some  mica  is  often  present  in  these  two  species  of 
rocks;  but  the  mica  in  diorite  is  generally  light  colored  (musco- 


54  GEOLOGICAL   STUDIES. 

vite),  while  that  in  norite  is  black  (biotite).  Some  quartz,  also, 
may  be  present  in  diorite,  and  then  it  is  called  quartz  diorite. 
Accordingly,  if  we  have  a  rock  containing  hornblende  and  a 
plagioclase  we  may  consider  the  plagioclase  acidic,  if  quartz  or 
light  mica  is  present;  and  basic,  if  no  quartz  is  present,  and 
especially  if  some  black  mica  is  present.  In  the  former  case  the 
rock  is  diorite;  in  the  latter,  norite.  Diorites  and  norites  pre- 
sent all  degrees  of  fineness;  and  when  they  are  too  fine  for  the 
constituent  minerals  to  be  seen  with  a  magnifier,  the  texture  is 
microcrystalline  or  cryptocrystalline  —  the  latter  term  denoting 
a  finer  texture  than  the  former.  The  rock  is  then  a  variety  of 
aphanite —  another  variety  being  almost  pure  hornblende.  Bed- 
ded aphanite  is  aphanite  schist. 

But  suppose  the  dark  mineral  in  a  quartzless  granite-like  rock 
proves  to  be  augite  instead  of  hornblende.  Now  we  may  remem- 
ber that  augite,  as  a  basic  mineral,  likes  to  associate  with  basic 
feldspars.  Therefore  in  this  case  the  feldspar  is  basic;  that  is, 
it  is  not  orthoclase  nor  an  acidic  plagioclase;  it  is  probably  a 
basic  plagioclase  like  labradorite  and  anorthite.  Now  augite 
and  a  basic  plagioclase  form  norite  and  diabase.  (For  particulars, 
see  Table,  Study  XIV.)  Occasionally,  however,  we  find  augite 
with  an  acidic  plagioclase,  like  oligoclase;  but  for  this  we  have  no 
different  name;  it  is  a  section  of  diabase.  But  we  do  not  find 
augite  with  acidic  orthoclase.  Remember  then:  If  you  have 
determined  augite,  the  feldspar  with  it  is  a  plagioclase  and  proba- 
bly a  basic  plagioclase. 

When  any  of  the  foregoing  rocks  present  themselves  in  a 
thick-bedded  condition,  they  are  gneissoid;  and  for  their  descrip- 
tion we  may  employ  the  terms  hyposyenite  gneiss,  diorite  gneiss, 
norite  gneiss,  and  diabase  gneiss.  Similarly,  any  of  these  may 
also  present  a  schistose  structure;  but  it  is  not  to  be  certainly 
concluded  from  this  structure  that  such  rocks  have  had  a  sedi- 
mentary origin,  like  common  stratified  rocks.  That  is  still  a 
question. 

The  rocks  in  the  quartzless  series  are  generally  dark-colored; 
but  not  always.  We  may  have  a  white  plagioclase  in  great  abun- 


MICACEOUS,    AMPHIBOLIC,    AND    PYROXENIC    ROCKS.          55 

dance,  and  but  little  hornblende  or  augite.  The  mixture  of  light 
and  dark  minerals  results  in  a  mottled  or  speckled,  or  "pepper- 
and-salt"  appearance. 

The  rocks  which  we  have  been  considering  illustrate  well  the 
principles  of  mineral  association.  The  companions  of  quartz  are 
mica,  orthoclase,  and  hornblende  —  not  plagioclase  (except  albite) 
and  augite.  The  companions  of  augite  are  the  more  basic  pla- 
gioclases.  Hornblende  prefers  biotite  to  muscovite;  but  not  al- 
ways. Thus  biotite  is  found  with  basic  plagioclase  in  norite, 
while  the  more  acidic  muscovite  is  found  with  the  acidic  plagio- 
clase in  diorite. 

EXERCISE. 

What  is  lacking  in  greisen  to  make  it  granite?  What  is  lacking  in 
granulite  to  make  it  granite?  What  would  result  from  uniting  greisen  and 
granulite?  What  should  we  name  an  unstratified  rock  composed  of  quartz, 
feldspar,  mica,  and  a  little  hornblende?  What,  if  it  is  quartz,  feldspar,  and 
hornblende  with  a  little  mica?  If  we  have  quartz  and  feldspar  together  with 
a  non-micaceous  dark  mineral,  what,  probably,  is  the  latter?  If  we  have 
quartz,  muscovite,  and  a  feldspar  together,  what,  probably,  is  the  feldspar? 
If  we  have  quartz,  hornblende,  and  a  mica,  what,  probably,  is  the  mica?  If 
we  have  plagioclase  and  a  mica,  is  the  latter  likely  to  be  light  or  dark 
colored  ?  Suppose  the  muscovite  of  a  granite  changes  to  hydromica,  what 
does  the  rock  become?  If  the  pyroxene  of  a  diabase  changes  to  hornblende, 
what  does  the  rock  become?  If  the  quartz  disappears  from  syenite,  what 
does  the  rock  become?  What  change  would  convert  hyposyenite  to  diorite? 
What  would  convert  diorite  to  diabase?  What  would  convert  diabase  to 
norite?  What  are  the  uses  of  syenite?  Wliich  is  most  durable,  syenite  or 
granite?  Syenite  or  diorite?  Coarse  or  fine  granite?  A  basic  or  an  acidic 
rock  ?  Which  weathers  most  rapidly,  feldspar  or  quartz  ?  Name  several  dif- 
ferent varieties  of  granite.  What  does  feldspar  become  on  decomposing? 

SUGGESTION. — The  varying  composition  of  the  granular  rocks  thus  far 
studied  furnishes  an  interesting  opportunity  for  a  geological  game.  Prepare 
a  quantity  of  cubical  blocks  of  hard  wood,  half  an  inch  or  so  in  diameter. 
To  a  number  of  these  attach  tickets  bearing  the  name  of  Quartz.  To  others 
attach  tickets  bearing  the  names  of  the  other  minerals  occuring  in  the  granu- 
lar rocks.  Then  select  two  or  three  minerals  (blocks),  and  lay  them  side  by 
side,  and  see  which  one  of  a  company  can  soonest  tell  what  rock  they  repre- 
sent. Let  some  umpire,  with  a  supply  of  checks  of  any  kind,  supply  the 
quickest  correct  respondent  in  each  case  with  a  check.  When  a  given  sup- 
ply of,  say,  fifty  checks  is  thus  exhausted,  let  the  number  in  each  individual's 


56  GEOLOGICAL   STUDIES. 

possession  be  counted,  and  let  the  one  having  most  checks  be  declared  the 
winner  of  the  game.  On  the  same  or  future  occasions  other  games  may  be 
played,  and  the  first  to  win  ten  games  may  be  declared  entitled  to  a  prize  — 
whatever  may  be  agreed  upon  and  provided  beforehand.  In  case  of  appeal 
from  the  decision  of  the  umpire,  reference  may  be  made  to  one  of  the  tables 
beyond.  This  suggestion  relates  thus  far  to  massive  granular  rocks.  But 
when  it  becomes  desirable  to  make  the  game  a  little  more  difficult,  the  re- 
spondent may  be  required  to  state  also  what  the  rock  would  be  if  thick- 
bedded,  and  what  if  thin-bedded.  The  following  minerals  are  suggested  to 
begin  with  :  quartz,  orthoclase,  acidic  plagioclase,  basic  plagioclase,  musco- 
vite,  biotite,  hornblende,  augite,  talc,  chlorite. 


STUDY  XI. — Felsitic,  Hydro  us -Magnesian,  and  Aluminous 

Rocks. 

I.     Felsitic  Rocks. 

We  have  picked  up  from  time  to  time  various  round,  smooth, 
and  exceedingly  fine-grained  bowlders,  to  which  we  ought  now  to 
direct  our  attention.  While  the  rocks  which  we  have  heretofore 
studied  are  sufficiently  coarse-grained  to  enable  us  to  inspect  their 
mineral  constituents  with  the  naked  eye,  or  at  least  with  a  pocket 
lens,  these  are  too  fine  for  that  method  of  study.  The  former  are 
phanerocrystalline  •  these  are  microcrystalline  or  cryptocrystal- 
line,  and  their  texture  can  only  be  seen  under  a  compound  micro- 
scope by  the  use  of  thin,  transparent  sections.  Their  composition 
may  also  be  learned  through  chemical  analyses.  But  we  do  not 
propose  to  resort  to  either  of  these  methods.  We  must  simply 
see  what  can  be  done  without  them. 

We  can  at  least  distinguish  colors.  Let  us  separate  the  black 
and  greenish-black  specimens  from  those  of  other  colors.  These 
are  chiefly  aphanites  •  and  we  have  studied  them  in  connection 
with  other  rocks.  Some  of  them  can  be  slightly  scratched,  while 
others  are  as  hard  as  orthoclase.  The  former  are  composed  chiefly 
of  hornblende,  and  might  be  styled  aphanitic  amphibolite,  or 
amphibolic  aphanite.  These  which  are  so  flinty  in  hardness 
evidently  contain  quartz  in  intimate  union  with  a  dark  min- 


FELSITIC,    HYDROUS-MAGNESIAN,  AND    ALUMINOUS   ROCKS.  57 

eral.  The  principal  dark  minerals  are  hornblende,  augite,  and 
labradorite.  But  quartz  and  labradorite  have  little  to  do  with 
each  other  ;  and  of  the  other  two,  quartz  prefers  hornblende. 
We  may  presume,  therefore,  that  this  flinty  aphanite  contains 
quartz  and  hornblende.  But  as  quartz  and  hornblende  do  not 
much  associate,  except  in  company  of  an  acidic  feldspar,  we  may 
further  conclude  that  the  real  mineral  constituents  of  this  apha- 
nite are  either  hornblende,  quartz,  and  orthoclase,  or  hornblende, 
quartz,  and  albite  or  oligoclase.  Now,  the  former  triplet  gives  us 
syenitic  aphanite,  and  the  latter,  diorUic  aphanite.  This  reason- 
ing is  validated  by  the  other  modes  of  study. 

Now  let  us  take  up  the  rnicrocrystalline  specimens  which  pre- 
sent whitish,  grayish,  and  reddish  colors.  Give  attention,  first, 
to  those  of  nearly  uniform  color.  We  shall  be  able  to  conclude, 
after  carefully  testing  the  different  specimens,  that  they  differ 
slightly  in  hardness,  like  the  aphanites.  If  we  can  make  a  dis- 
crimination of  this  kind,  let  us  take,  first,  the  hardest.  Now, 
these  are  as  hard  as  quartz,  and  there  is  no  mineral  but  quartz 
which  is  likely  to  be  abundant  enough  to  supply  these  rocks. 
But  these  are  not  pure  quartz  ;  they  have  not  the  glassy  lustre 
of  quartz.  They  do,  indeed,  suggest  the  jaspers,  but  there  is  an- 
other alternative  :  they  may  contain  feldspar,  intimately  mixed 
with  the  quartz.  But,  as  before,  it  must  be  an  acidic  feldspar  — 
probably  orthoclase.  Now,  other  examinations  corroborate  this 
induction.  This  is,  then,  simply  a  flinty,  amorphous  feldspar.  It 
has  received  the  name  petrosilex,  sometimes  also  known  as  hal- 
leflinta,  or  false  flint  (Swedish,  pronounced  nearly  helleftinta). 

Taking,  next,  the  reddish  or  whitish  specimen,  we  find  that 
it  has  the  hardness  and  lustre  of  feldspar,  though  it  shows  no 
cleavage  faces.  We  can  do  no  more.  It  seems  to  be  a  compact, 
amorphous  feldspar.  Other  investigations  show  it  to  be  chiefly 
a  plagioclase.  It  is  called  felsite.  Petrosilex  is  also  felsitic,  and 
by  some  is  not  separated  from  felsite. 

Let  us  now  give  attention  to  the  specimens  separated  as  not 
having  homogeneous  colors.  Our  notice  is  at  once  attracted  by 
the  fact  that  they  consist  of  a  fine,  homogeneous  base  or  matrix, 


58  GEOLOGICAL   STUDIES. 

in  which  other  minerals  are  imbedded.  By  testing  for  hardness, 
as  before,  we  find  that  this  base  by  itself  is  sometimes  a  felsite, 
and  sometimes  a  petrosilex.  Without  regard  to  this  distinction, 
let  us  study  the  imbedded  minerals.  In  one  specimen  they  are 
clearly  crystals  of  feldspar.  Now,  crystals  of  any  kind,  imbedded 
in  a  homogeneous  feldspathic  matrix,  form  a  porphyritic  rock. 
This  is,  then,  a  porphyritic  felsite,  and  this  porphyritic  rock  is 
the  typical  porphyry.  Notice  the  colors  —  reddish  or  grayish 
base,  with  white  crystals  imbedded. 

If  we  find  imbedded  crystals  or  fragments  of  quartz,  the  rock 
is  a  quartz  porphyry  •  and  if  we  find  rounded  pebbles  thus  imbed- 
ded, the  rock  is  a  conglomerate  porphyry.  This  unusual  vari- 
ety of  porphyry  we  shall  probably  not  meet  with.  It  forms,  how- 
ever, the  porphyry  point  at  Marblehead,  Massachusetts.  Other 

porphyries  may  be  seen  at  Lynn 
and  Nahant,  and  they  are  very 
common  around  the  shores  of  Lake 
Superior.  (See  Fig.  8.)  Other  kinds 
of  rocks,  also,  besides  felsites,  are 
often  found  porphyritic.  Figure 
FIG.  24—PoRpHYRiTic  GRANITE,  34  shows  a  porphyritic  granite. 

from  Land's  End,  England. 

II.     Hydrous -Mag-nesian  Rocks. 

Let  us  now  direct  attention  to  the  Hydrous-Magnesian  Rocks. 
These,  as  will  be  inferred,  are  characterized  by  the  presence  of 
the  hydrous-magnesian  minerals.  If  you  turn  to  the  table  of 
composition  of  minerals,  on  page  40,  you  will  perceive  that  all 
these  minerals  range  low  in  respect  to  hardness.  They  must, 
therefore,  impart  a  moderate  hardness  to  the  rocks.  You  will  no- 
tice further  that  they  are  less  rich  in  iron  than  the  dark-colored 
minerals.  Hence  the  rocks  which  they  form  will  be  of  light  col- 
ors and  of  low  specific  gravity.  Now,  in  consequence  of  this 
comparative  softness,  we  cannot  expect  bowlders  of  these  rocks  to 
have  lasted  through  the  wear  and  tear  of  geologic  time,  like  the 
bowlders  of  harder  rocks.  For  these  reasons  the  student  may 


FELSITIC,    HYDROUS-MAGNESIAS,  AND   ALUMINOUS   ROCKS.  59 

have  to  depend  partly  on  descriptions.  Still,  there  are  some 
of  this  class  which,  from  the  quartz  contained,  have  lasted  to  our 
time.  One  of  these,  protogine,  consisting  of  quartz,  feldspar 
and  talc,  in  a  massive  state,  is  not  often  met  in  this  country  ;  but 
it  forms  the  central  mass  of  the  high  Alps  of  central  Europe,  and 
rounded  masses  are  often  seen  borne  to  the  lower  levels  by  gla- 
ciers. Protogine  occurs  sparingly  in  the  northwestern  states. 
In  bedded  conditions  it  gives  us  protogine  gneiss  and  protogine 
schist.  The  last  is  not  essentially  different  from  talcose  schist. 
The  latter,  however,  as  we  actually  find  it,  consists  almost  wholly 
of  minute  folia  of  talc.  It  is  a  rare  rock,  though  occurring  near 
Marquette,  Mich.,  at  various  localities  in  northern  New  York, 
and  in  other  regions.  But  it  must  no  longer  be  confounded  with 
the  sericite  schist,  or  hydromica  schist,  which  was  till  recently 
mistaken  for  talc  schist. 

Every  one  is  acquainted  with  the  so-called  <:  soapstone  "  grid- 
dles, and  the  slabs  of  "soapstone"  used  for  foot-warmers  —  their 
power  of  retaining  heat  being  very  great.  This  soapstone  is  the 
steatite  of  the  geologist,  and  consists  essentially  of  grayish,  com- 
pact, amorphous  talc.  It  is  soapy  to  the  feel,  and  is  easily  cut 
with  a  knife.  When  quite  pure  it  is  milk  white,  and  forms  the 
article  known  as  "  French  chalk."  The  uses  of  steatite  are  quite 
numerous.  Slabs  of  it  are  employed  for  fire  stones  in  furnaces 
and  in  stoves.  The  fine-grained  varieties  are  carved  into  orna- 
ments. Inkstands  are  often  made  from  it,  especially  the  white 
variety.  Ground  steatite  is  employed  for  diminishing  friction, 
and  the  manufacture  of  porcelain  and  the  removal  of  oil  stains 
furnish  other  uses.  The  so-called  "  soapstone "  of  the  artesian 
well-borer  is  merely  an  unctuous,  partially  indurated  clay. 

Next,  there  are  the  chloritic  rocks.  Chlorite  schist  occurs  in 
the  mining  regions  of  Lake  Superior.  It  is  a  dark-greenish, 
greasy  looking  rock,  in  which  chlorite,  in  closely  aggregated  or 
interwoven  folia,  is  the  chief,  sometimes  nearly  the  sole,  constitu- 
ent, while  quartz  is  generally  the  principal  ground  mass.  The 
feldspars,  however,  enter  into  this  schist  in  about  the  same  pro- 
portions as  in  mica  and  hornblende  schists.  By  increase  of  the 


60  GEOLOGICAL   STUDIES. 

feldspar,  accompanied  by  a  heavier  bedding,  this  schist  graduates 
into  chloritic  gneiss.  In  the  opposite  direction  it  graduates  into 
chlorite  slate,  a  fine  slaty  rock,  containing  some  aluminous  mat- 
ter. A  rock  composed  mostly  of  chlorite  is  called,  also,  chlorite 
rock. 

III.     Aluminous  Hocks. 

Passing  to  aluminous  rocks,  we  have  first  the  fine  white  slate, 
composed  of  pyrophyllite,  and  having  the  softness,  appearance 
and  soapy  feel  of  the  talcose  rocks,  and  known  as  pyrophyllite 
slate.  It  occurs  in  place  in  North  Carolina,  and  one  of  the  va- 
rieties is  employed  in  making  slate-pencils.  But  the  greater 
number  of  aluminous  rocks  are  characterized  by  a  clayey  constitu- 
ent, the  basis  of  which  is  kaolinite.  When  the  material  is  un- 
consolidated  and  comparatively  pure,  it  forms  kaolin,  extensively 
used  in  porcelain  making.  When  mixed  with  various  impurities, 
and  more  or  less  silica,  it  constitutes  common  clay.  This  is  some- 
times dark,  or  even  black,  from  the  abundance  of  carbonaceous 
matter.  It  is  sometimes  reddish,  bluish  or  whitish,  depending  on 
purity  and  the  nature  of  the  impurities.  The  burning  of  clay 
not  only  hardens  it,  but  generally  imparts  a  reddish  color, 
through  the  peroxidation  of  the  iron.  If,  however,  the  iron  ex- 
ists as  a  silicate,  no  reddening  takes  place.  This  is  the  character 
of  the  "  Milwaukee  brick,"  so-called;  though  this  sort  of  clay  is 
extensively  distributed  throughout  the  lake  region.  Fire  clay 
is  a  clay  free  from  iron,  lime  or  other  substance  which  would  pro- 
mote fusion;  and  is  therefore  capable  of  resisting  intense  heat. 
It  generally  contains  much  arenaceous  matter,  which  prevents 
shrinkage  and  warping  of  the  fire-brick. 

When  clay  with  more  or  less  arenaceous  or  silicious  matter 
has  become  somewhat  indurated,  it  assumes  the  character  of  a 
shale,  a  rock  which  easily  splits  into  somewhat  even  flakes,  and 
presents  many  varieties  in  composition  and  color.  Perhaps  the 
most  accessible  examples  are  the  dark  shale  fragments  often 
found  mixed  with  our  supply  of  coal.  Most  shales  are  dark,  and 
many  are  even  black,  from  the  abundance  of  carbonaceous  mat- 


CALCAREOUS   ROCKS.  61 

ter  contained  in  them.  The  carbon,  under  such  conditions,  pos- 
sesses a  strong  predisposition  to  unite  with  hydrogen  and  pass 
into  bitumen. 

When,  finally,  the  clayey  rock  has  been  firmly  hardened,  it 
constitutes  argillite  or  clay  slate,  called  sometimes  phyllite.  In 
color  it  is  bluish,  whitish,  reddish  or  greenish.  It  splits  into  thin, 
even  layers,  and  is  extensively  employed  for  roofing  and  for  writ- 
ing slates.  Argillites  are  almost  microcrystalline;  but  in  some 
cases  we  find  them  graduating  into  a  very  fine  mica  schist  or 
hydromica  schist;  and  in  others,  by  a  large  accession  of  extremely 
fine  arenaceous  matter,  they  become  novaculite  or  "  oil-stone." 

EXERCISES. 

How  does  petrosilex  differ  in  composition  from  felsite  proper?  How 
does  it  differ  from  aphanite?  What  is  the  difference  between  a  porphyritic 
granitic  and  a  granitic  porphyry?  Which  is  most  basic,  felsite  proper  or 
petrosilex?  What  is  the  difference  between  kaolin  and  felsite?  What  is  the 
effect  of  intense  heat  upon  clay?  What  is  the  effect  on  kaolin?  Give  an  ex- 
ample of  burned  kaolin.  Is  it  opaque  or  translucent?  How  might  it  have 
been  made  more  translucent?  What  is  the  difference  between  porcelain  and 
felsite?  Which  contains  most  alkali,  kaolin  or  orthoclase?  What  causes 
burnt  clay  sometimes  to  be  vitrified?  What  kind  of  clay  would  not  vitrify? 
What  are  un verifiable  clays  used  for?  What  is  the  effect  of  limestone  peb- 
bles in  brick  clay?  What  causes  some  bricks  to  "  slack  "?  What  causes  the 
dark  color  of  aphanite?  What  causes  its  hardness?  If  the  hornblende 
should  be  removed  from  dioritic  aphanite  what  would  it  become?  What  is 
the  difference  between  pyrophyllite  slate  and  talcose  slate?  Between  talcose 
slate  and  steatite?  Between  protogine  and  granite?  Between  syenite  and 
augite-syenite?  What  class  of  crystalline  rocks  is  not  likely  to  be  found  as 
bowlders?  Why  not?  Why  are  bowlders  predominantly  quartzose?  Men- 
tion four  or  more  different  rocks  or  minerals  used  for  making  colored 
marks.  What  change  must  be  made  to  convert  norite  into  diabase? 


STUDY  XII.—  Calcareous  Rocks. 

Let  us  get  together  samples  of  the  common  rocks  which 
effervesce  on  the  application  of  acid,  with  or  without  heat. 
They  are  composed  essentially  of  calcite  and  dolomite.  We  ob- 


62  GEOLOGICAL   STUDIES. 

tain  them  at  the  stone  cutter's,  from  broken  articles  in  marble, 
from  among  certain  building  materials,  and  occasionally  among 
surface  bowlders.  If  any  limestone  or  marble  ledges  exist  in  the 
vicinity,  we  shall,  of  course,  obtain  specimens  from  the  rocks  in 
place. 

With  our  assortment  before  us,  we  notice  at  once  that  some 
of  the  specimens  are  brighter  and  more  lustrous,  others  are  duller 
and  more  earthy.  The  former  are  cystalline,  the  latter  uncrystal- 
line.  The  former  are  purer,  the  latter  have  admixtures  of  vari- 
ous accessory  ingredients.  The  former  we  call  marbles;  the 
latter,  limestones.  The  marbles  are  thick-bedded  and  have  hard- 
ness and  homogeneity,  and  freedom  from  cracks  and  cavities. 
They  can  be  cut  and  polished.  The  limestones  are  thick-  or  thin- 
bedded;  but  they  are  not  homogeneous,  and  generally  contain 
fissures  and  cavities.  They  cannot  be  advantageously  cut  into 
slabs  and  polished.  Some  limestones,  however,  without  being 
crystalline,  are  sufficiently  thick-bedded  and  homogeneous  to  be 
sawed  and  polished;  and  when  they  contain  many  fossil  shells, 
encrinites  or  corals,  the  polished  surfaces  are  handsome.  Such 
marbles  are  known  as  shell  marble. 

Of  the  crystalline,  heavy-bedded  marbles  we  have  endless  va- 
rieties of  color  and  texture.  The  granular,  white  sorts  are 
called  saccharoidal.  Fine  white,  even-grained  sorts  are  statu- 
ary marble,  of  which  the  most  celebrated  quarries  are  the  Pa- 
rian and  Pentelican,  in  Greece,  and  those  of  Carrara,  in  Italy. 
By  the  dissemination  of  streaks  of  aluminous  matter,  clouded 
marbles  are  produced,  which  are  common  in  Vermont.  An 
abundance  of  bituminous  matter  makes  a  black  or  Egyptian  mar- 
ble which  also  occurs  in  Vermont.  It  may  be  varied  with  lighter 
matter.  Some  good  marbles  are  calcareous  conglomerates.  A 
much  admired  sort  is  quarried  in  eastern  Tennessee,  and  is  used 
for  pillars  in  public  buildings.  Verd  antique  marble  is  a  dark 
green  serpentine  clouded  and  varied  with  lighter  calcite. 

Of  the  uncrystalline,  lustreless  limestones  we  find  also  endless 
varieties.  They  are  caused  chiefly  by  the  variations  in  the  im- 
purities. Sometimes  an  inspection  of  a  freshly  broken  surface 


CALCAREOUS    ROCKS.  63 

shows  a  sparry  constitution,  somewhat  approaching  that  of  a 
marble.  Very  frequently  limestones  are  more  or  less  saturated 
with  petroleum,  which  gives  them  a  brown  or  very  dark  color. 
Black  limestones  contain  carbonaceous  matter.  Bluish  and  ashen 
limestones  are  argillaceous.  Yellowish  and  reddish  limestones 
are  ferruginous.  Sometimes  grains  of  sand  are  disseminated 
through  a  limestone,  which  is  then  arenaceous.  If  silicious  mat- 
ter not  in  an  arenaceous  state  is  intimately  mixed  or  combined 
with  the  calcareous,  the  limestone  is  silicious.  If  alumina  is  so 
combined  the  limestone  is  aluminous.  Distinguish  particularly 
argillaceous  and  arenaceous  from  aluminous  and  silicious.  The 
first  two  terms  imply  the  material  in  a  somewhat  isolated  and 
visible  state;  the  other  two  imply  it  intimately  commingled,  or 
perhaps  chemically  combined. 

Many  limestones  are  rnagnesian.  They  do  not  effervesce 
freely.  Let  us  pick  out  such  from  our  collection.  They  do  not 
look  very  different  from  the  others.  Most  of  the  great  western 
limestone  formations,  so  called,  are  magnesian,  or  even  dolomitic 
—  that  is,  about  one-half  carbonate  of  magnesia  (see  the  Table  of 
Compositions,  page  40).  Though  dolomites  are  not  properly  sepa- 
rable by  their  color,  it  happens,  as  a  fact,  that  most  of  the  west- 
ern dolomites  present  a  buffish  hue.  This  is  especially  the  case 
with  the  "lower  magnesian  limestone"  which  helps  to  form  the 
cliffs  along  the  Upper  Mississippi.  The  observation  may  also  be 
made  in  Missouri  and  Michigan.  As  a  fact,  it  is  further  observ- 
able that  many  dolomites  and  dolomitic  limestones  have  a  finely 
granular  texture.  In  fact,  they  have  been  sometimes  reported  as 
sandstones.  So  the  buff  color  and  granular  texture  may  be  taken 
as  a  preliminary  indication  of  a  dolomitic  formation.  Slowness  of 
effervescence  is  confirmatory.  Beyond  this  we  cannot  go  without 
chemical  analysis. 

You  have,  perhaps,  noticed  some  limestone  containing  small, 
spherical  pellets,  like  homo3opathic  pills.  Such  limestone  is 
oolitic  (not  pronounced  oo-litic).  Such  pellets  sometimes  com- 
pose the  entire  rock,  which  is  then  an  oolite.  Examination  of 
these  spherules  broken  through  the  middle  reveals  a  concentric 


64  GEOLOGICAL   STUDIES. 

structure.  It  is  then  a  "  concretion,"  similar  to  the  concretionary 
"  iron-stone  "  before  mentioned.  When  the  concretions  are  larger 
the  rock  is  pisolitic. 

Limestones  have  no  standard  degree  of  hardness.  All  may 
be  easily  scratched;  but  in  the  Gulf  States  are  limestones  which 
may  be  cut  with  the  knife.  One  of  these  is  the  widely  known 
"rotten  limestone";  another  is  the  so  called  "white  limestone." 
But  they  are  harder  than  chalk,  and,  besides,  have  "grit"  dis- 
seminated through  them.  Some  chalk  is  pretty  free  from  grit, 
though  it  abounds  in  nodules  of  flint.  It  does  not  occur  in 
America,  but  comes  chiefly  from  England  and  France.  "  Whit- 
ing "  and  "  Spanish  white  "  are  prepared  from  it.  Marl  may  be 
described  as  unconsolidated  chalk.  We  have  already  learned  (in 
Study  II  —  but  see  especially  Study  XV),  how  it  is  deposited. 
We  have  learned,  also,  of  the  origin  of  travertin  and  tufa. 
When  calcareous  waters  drip  from  the  roof  of  a  cavern,  the  de- 
posit formed  on  the  floor  is  stalagmite  ;  and  the  icicle-like  form 
pendant  from  the  roof  is  a  stalactite.  The  banded  colorations  in 
stalagmite  fit  it  for  many  ornamental  uses. 

All  calcareous  rocks  are  slightly  soluble  in  meteoric  (or  atmos- 
pheric) waters;  hence,  when  used  in  architecture  or  art,  in  ex- 
posed situations,  they  possess  a  limited  durability.  The  slow 
decay  of  limestones  and  marbles  may  be  noticed  in  some  of  our 
oldest  structures.  Marble  cemetery  slabs  or  monuments,  one  or 
two  hundred  years  old,  are  distinctly  weathered.  On  the  dome 
of  St.  Paul's  Cathedral,  London,  the  weathered,  earthv  limestone 
has  retreated  a  quarter  of  an  inch,  leaving  the  silicified  fossils 
projecting  to  that  extent.  Yet  many  of  the  ancient  statues  and 
columns  buried  in  the  earth  have  retained  admirable  perfection. 
In  the  ruined  but  famous  Palace  of  the  Oassars,  at  Rome,  the 
architectural  carvings  retain  striking  sharpness  and  distinctness, 
after  two  thousand  years  of  exjposure.  On  the  other  hand,  most 
of  the  caverns  of  the  world  are  attestations  of  the  solubility  of 
limestone.  They  began  as  fissures,  through  which  streams  of 
water  passed,  dissolving  continually  —  and  also  wearing  —  the 
limestone  surfaces.  That  such  works  have  been  long  in  progress 


CALCAREOUS   ROCKS.  65 

is  evidenced  by  the  slow  yielding  of  calcareous  surfaces  during 
historic  times. 

Limestones,  considered  in  reference  to  their  fitness  for  build- 
ing, should  be  examined  as  to  their  power  of  absorbing  and  retain- 
ing water.  A  saturated  limestone  subjected  to  freezing  is  liable 
to  crumble,  or  even  to  be  completely  shattered.  Hence,  argilla- 
ceous and  aluminous  limestones  are  quite  unsuitable  for  situations 
exposed  to  the  weather.  Some  of  the  latter,  presenting  a  fine- 
grained, massive,  and  substantial  appearance  when  issuing  from 
the  quarry,  may  be  reduced  to  a  state  of  ruin  by  the  frosts  of  a 
single  winter. 

A  hydraulic  limestone  is  one  which  contains  a  considerable 
percentage  (fifteen  to  thirty  per  cent)  of  clay  or  magnesia,  or 
both  together.  Calcination  renders  the  silica  of  the  clay  soluble 
at  the  same  time  that  the  carbonic  acid  is  expelled  from  the  car- 
bonate of  lime.  Contact  with  water,  therefore,  dissolves  the 
silica,  and  this,  with  the  quicklime,  slowly  forms  a  hydrous  sili- 
cate of  lime,  which  is  firm  and  insoluble.  Another  portion  of  the 
silica  forms  a  silicate  of  alumina;  and  if  magnesia  be  present,  a 
silicate  of  magnesia  also  results. 

Gypsum  is  a  calcareous  rock  of  much  importance,  having 
most  of  the  properties  of  the  mineral  gypsum,  already  studied. 
We  find  it  mixed  in  all  proportions  with  argillaceous  matter,  and 
sometimes  disseminated  richly  through  argillaceous  limestones. 
It  also  occurs  in  stratified  beds  of  great  or  small  extent.  Some- 
times the  original  bed  has  been  dissolved  away,  and  only  some 
lenticular  remnants  of  it  are  found.  Often,  also,  the  disappear- 
ance of  a  gypsum  bed  occasions  "sink  holes"  at  the  surface. 
Such  holes,  then,  seem  to  indicate  the  presence  of  an  underlying 
soluble  stratum,  probably  gypsum.  But  they  must  be  carefully 
distinguished  from  mere  depressions  in  'the  drift,  sometimes 
called  "potash  kettles."  Much  of  the  gypsum  found  in  the  crude 
condition  contains  a  considerable  admixture  of  clay,  and  pos- 
sesses a  bluish  color.  In  other  situations  —  as  at  Grand  Rapids 
and  Alabaster,  Mich. —  beds  of  gypsum  exist  in  a  state  of 
great  purity,  and  then  it  exhibits  a  crystalline  texture.  White, 


66  GEOLOGICAL   STUDIES. 

granular  deposits  afford  snoivy  gypsum.  Gypsum  equally  fine 
and  uniform  is  often  tinted  with  rich  colors.  Fine  gypsum, 
capable  of  forming  ornaments,  is  known  as  alabaster.  It  may  be 
white  or  colored.  Near  Grand  Rapids,  in  Michigan,  are  extensive 
beds  of  pure  gypsum,  having  largely  a  coarse  fibrous  structure. 
Some  portions,  however,  are  granular.  This  formation  seems  to 
extend  under  the  central  part  of  the  state,  for  it  reappears  on 
Saginaw  Bay,  where  it  is  also  extensively  quarried.  Other 
sources  of  commercial  gypsum  are  on  the  border  of  Sandusky  Bay, 
Ohio,  and  in  central-western  New  York.  It  is  abundant,  also,  in 
Virginia,  Tennessee  and  Arkansas.  Very  fine  and  extensive 
deposits  exist  in  Nova  Scotia.  Gypsum  is  widely  employed  as 
an  agricultural  fertilizer,  also  as  a  plaster  for  "hard  finish,"  and 
also  in  the  preparation  of  "moulds"  and  "casts." 

EXERCISES. 

What  change  does  calcined  gypsum  undergo  when  long  exposed  to  the 
air?  What  change  does  quicklime  undergo  when  so  exposed?  Which  is 
most  impaired  by  mere  dampness?  How  does  dampness  affect  water-lime? 
Why  might  not  water-limestone  calcined  at  a  white  heat  make  a  good 
cement?  Explain  how  a  water-lime  might  be  prepared  from  pure  caus- 
tic lime.  Would  caustic  lime  and  pure  sand  make  a  cement?  Why  do  you 
give  this  answer?  Would  caustic  lime  and  clay  make  a  cement?  Why 
this  answer?  How  is  silica  made  soluble?  What  is  the  use  of  insoluble 
silica  in  a  cement?  Which  most  rapidly  dissolves,  gypsum  or  limestone? 
Why  did  the  "Cardiff  giant,"  made  of  gypsum,  possess  an  ancient  appear- 
ance after  a  few  months'  burial?  What  is  the  source  of  rust  stains  on  the 
surface  of  some  marbles?  Have  you  any  specimens  from  any  cavern? 
Describe  them.  How  might  human  bones  become  buried  in  stalagmite? 
Have  you  ever  heard  of  such  a  case?  Have  you  ever  heard  of  bones  buried 
in  travertin?  Mention  some  extensive  deposits  of  travertin.  How  does 
travertin  differ  from  common  limestone?  How  would  slabs  of  alabaster 
serve  as  an  external  veneering  for  house  fronts?  By  what  means  may  plas- 
ter casts  be  rendered  harder  than  results  from  the  simple  "setting"  of  the 
plaster? 


CARBONACEOUS   ROCKS.  67 

STUDY   XIII. —  Carbonaceous  and  Iron  Ore  Rocks. 
I.     Carbonaceous  Kocks. 

Coal  is  something  so  familiar  that  a  brief  study  will  make  us 
acquainted  with  its  physical  characters  and  modes  of  occurrence. 
Its  geological  history  must,  of  course,  be  taken  up  in  another 
connection.  You  have  seen  the  "soft coal"  burning  on  the  grate, 
and  have  noticed  the  escape  of  inflammable  and  other  gases;  and 
have  also  detected  the  peculiar  empyreumatic  odor  which  bitu- 
minous coal  emits.  You  have  seen  the  gas-making  coal  put  in 
the  retorts  at  the  gas  works,  and  thus  received  other  evidence 
that  common  coal  contains  some  constituents  which  may  be 
driven  off  by  heat.  Now.  what  are  these  volatile  constituents, 
and  what  is  the  coal?  Manifestly  they  are  both  combustible. 
The  gas  burns  at  the  jet,  and  the  coal  and  gas  together  burn  on 
the  grate.  Even  the  coke  which  remains  in  the  retort  after  the 
gas  is  disengaged  is  also  combustible.  Now,  what  is  that  which 
is  combustible  in  common  air,  and  is  also  an  abundant  substance? 
It  is  carbon;  and  this  element,  therefore,  is  the  basis  of  all  the 
coals  and  the  inflammable  gases  derived  from  coals. 

If  we  call  the  chemist  to  our  aid,  he  informs  us  that  the  gases 
are  compounds  of  hydrogen  and  carbon;  and  so  are  the  coals, 
but  with  a  diminished  proportion  of  hydrogen,  and  the  addition 
of  oxygen.  He  informs  us,  also,  that  coal  tar  and  other  liquids 
derivable  from  coal,  such  as  naphtha  and  coal  oil,  are  other 
compounds  of  carbon  and  hydrogen.  We  observe,  also,  that 
the  coals  called  anthracite  contain  comparatively  little  of  the 
gaseous  and  fluid  hydrocarbons,  while  those  called  bituminous 
contain  larger  percentages — the  fixed  constituents  of  both  classes 
of  coals  being  essentially  carbon,  or  something  not  very  different 
from  charcoal. 

A  coal  from  which  all  volatile  constituents  have  been  expelled 
is  graphite  or  plumbago;  while  on  the  other  hand,  we  find  in 
nature  products  composed  of  the  liquid  constituents  occurring  in 
coal,  and  others  composed  of  the  gaseous  constituents.  The 


68  GEOLOGICAL   STUDIES. 

liquid  product  is  petroleum,  and  the  other  is  natural  inflammable 
gas.  The  petroleum  has  accumulated  in  reservoirs  in  the  rocks 
to  an  extent  which  becomes  a  great  natural  curiosity  —  some 
wells  having  discharged  five  thousand  gallons  a  day;  and  the  gas 
is  now  escaping  through  artesian  borings  in  such  enormous  sup- 
ply as  to  light  cities  and  furnish  fuel  for  great  manufacturing 
operations.  Pittsburgh  and  its  vicinity  are  especially  favored 
with  combustible  gas;  though  enormous  outflows  exist  in  Knox 
county,  Ohio,  and  in  various  other  regions.  Though  petroleum 
and  gas  may  be  artificially  produced  from  bituminous  coal,  it 
must  not  be  inferred  that  these  natural  products  have  been  so 
derived;  since  according  to  the  evidences,  no  connection  with 
coal  beds  usually  exists.  A  striking  proof  of  this  has  very 
recently  been  brought  to  light  in  northwestern  Ohio,  in  a  region 
at  least  eighty  miles  from  the  nearest  coal  field,  where  from  three 
wells  half  a  million  cubic  feet  of  inflammable  gas  are  obtained 
daily  from  a  geological  position  two  thousand  feet  or  more  below 
the  horizon  of  the  lowest  coal  (Orton).  Probably,  however,  like 
coal,  petroleum  and  inflammable  gases  have  had  an  organic 
origin.  (See,  further,  Study  XXIX.) 

When  petroleum  is  exposed  to  the  air  it  loses  its  volatile  con- 
stituents, and  the  fixed  residuum  is  asphalt.  Different  varieties 
of  asphaltic  products  have  thus  accumulated  in  deep  rock  fissures, 
and  they  are  known  by  such  names  as  albertite,  grahamite,  and 
others.  Succinite,  or  the  essential  part  of  amber,  is  an  oxygen- 
ated hydrocarbon,  which  may  be  mentioned  in  this  connection. 
It  is  believed  to  be  a  fossil  resin. 

Peat  you  may  find  accumulating  around  the  borders  of  lakes 
and  ponds.  (See  Fig.  25.)  Often  the  basins  of  old  lakes  are 
completely  filled  with  peat.  Manifestly  it  is  of  vegetable  origin. 
It  has  a  dark  brown  or  nearly  black  color.  It  is  combustible,  and 
emits,  like  coal,  an  empyreumatic  odor.  Some  old,  deeply  buried 
peats  closely  resemble  that  sort  of  coal  known  as  brown  coal, 
and  lignite.  These,  like  peat,  have  no  standard  purity.  They 
may  be  worth  more  or  less  as  fuel.  Peat,  however,  is  extensively 
employed  on  the  continent  of  Europe  in  porcelain  stoves  for 


IRON    ORE   ROCKS.  69 

warming  houses.  If  we  arrange  some  of  these  carbonaceous  and 
hydrocarbonaceous  substances  in  serial  order,  they  will  stand 
somewhat  as  follows  : 

1.  Gases.     Like  the  light  and  heavy  inflammable  gases. 

2.  Liquids.     Like  Naphtha,  Petroleum,  Benzole,  Tuluole,  etc. 

3.  Wctxy  Solids.     As  the  Paraffin e  and  Scheererite  groups  of 

substances. 

4.  Firm  Solids,     (a)  Asphaltic,  like  Asphalt,  Albertite,  Gra- 

hamite,  Torbanite  ;  (b)  Coaly — a  series  including  Peat, 
Lignite,  Bituminous  Coals,  Anthracite,  Graphite,  Dia- 
mond (?). 

II.     Iron  Ore  Rocks. 

On  visiting  any  iron  ore  mine  we  perceive  that  the  ore  occurs 
as  a  rock  more  or  less  distinctly  stratified.  We  find  the  ore  beds 
formed  from  the  three  principal  ores  already  studied.  They  form 
strata  like  the  other  rocks  with  which  they  are  associated.  Gen- 
erally, the  stratification  of  the  ore  is  quite  conspicuous.  Some- 
times, however,  the  beds  appear  to  wedge  out  in  all  directions, 
and  thus  to  terminate.  It  is  so  with  the  beds  at  Lake  Superior, 
in  northern  New  York,  in  Missouri,  and  elsewhere.  The  ores  in 
these  beds  are  mere  masses  of  haematite  schist,  or  magnetite 
schist,  and  the  kinds  are  distinguished  in  the  same  way  as  the 
minerals  bearing  these  names.  Great  beds  of  titanic  iron  ore 
also  exist  in  Canada  and  other  regions,  which  seem  to  be  substan- 
tially a  mixture  of  magnetite  and  oxide  of  titanium.  But  titanic 
ores  present  various  percentages  of  protoxide  and  peroxide  of 
iron  with  binoxide  of  titanium.  The  Franklinite  ores  of  New 
Jersey  consist  of  haematite  about  two-thirds,  and  oxide  of  zinc 
one-fourth,  the  remainder  being  manganese.  Sometimes  these 
great  iron-ore  masses  terminate  abruptly  against  the  "country 
rock  "  ;  but  often  they  disappear  by  gradual  increase  of  other 
rock  constituents.  The  accession  of  silica,  gives  rise  to  a  silicious 
ore  ;  then,  at  a  remoter  point,  to  a  lean  silicious  ore  ;  then,  to  a 
highly  ferruginous  jaspery  schist,  as  previously  explained,  and, 
finally,  an  ordinary  silicious  schist,  or  other  rock.  Mixed  with 


70  GEOLOGICAL   STUDIES. 

clay,  haematite  forms  argillaceous  haematite,  which  is  often  of  a 
deep  red  color,  varying  to  brownish  black.  It  has  sometimes  an 
oolitic  structure. 

Limonite  rocks  result  from  the  hydration  of  the  hrematite  and 
magnetite  schists,  and,  in  the  regions  just  named,  the  process  can 
sometimes  be  seen  incomplete.  Extensive  beds  exist  in  Salisbury 
and  Kent,  Conn.,  as  also  at  sundry  points  in  Dutchess  county,  N.  Y. 
At  Hinsdale,  Mass.,  it  occurs  as  the  cement  in  a  conglomerate 
quartz  rock.  The  commencement  of  such  a  process  of  cementa- 
tion of  pebbles  is  often  observed  in  the  limonitic  deposit  from 
springs.  These  deposits,  as  explained  in  Study  II,  give  rise  to 
extensive  beds  of  bog  iron  ore,  or  swamp  limonite.  One  of  the 
most  desirable  ores  of  iron  is  limonite,  since,  though  less  rich 
than  haematite  and  magnetite,  it  is  more  easily  reduced.  The  iron 
yielded  by  bog  ore,  however,  is  cold  short,  owing  to  the  presence 
of  phosphorus,  and  hence  cannot  be  employed  in  the  production 
of  wire,  or  even  of  sheet  iron.  For  casting  it  is  superior. 

Another  important  class  of  iron  ores  is  afforded  by  siderite, 
or  carbonate  of  iron.  It  is  generally  known  as  spathic  iron.  It 
occurs  in  gneiss,  mica  schist,  and  argillite,  sometimes  in  extensive 
beds,  as  in  Styria  and  Carinthia,  and  at  Plymouth,  in  Vermont, 
Sterling,  Mass.,  Antwerp  and  Rossie,  N.  Y.,  and  the  Fentress  and 
Harlem  rivers,  N.  C.  Siderite  is  often  found  united  with  argilla- 
ceous matter  in  the  form  of  nodules  (kidney-iron)  and  beds  (clay 
iron-stone),  especially  in  the  coal  regions  of  the  country,  though 
this  form  of  ore  exists  also  in  other  formations. 

III.     Eruptive  Rocks. 

That  such  rocks  as  sandstones,  limestones,  and  shale  have  had 
a  sedimentary  origin  is  apparent  from  the  bedded  arrangement 
of  their  materials  in  parallel  layers;  from  the  identity  of  those 
materials  with  the  sediments  gathering  over  modern  sea  bottoms, 
and  from  the  presence  in  them  of  so  many  relics  of  the  organisms 
of  the  sea  —  but  of  all  this  we  shall  learn  hereafter.  If  traces  of 
stratification  are  proofs  of  sedimentary  origin,  then  many  of  the 
crystalline  rocks  are  also  sedimentary.  All  the  schists  and 


ERUPTIVE    ROCKS.  71 

gneisses  are  stratified;  and  granite  sometimes  passes  by  contin- 
uity into  gneissoid  rocks.  But  lavas  erupted  from  Vesuvius  are 
not  sedimentary.  They  may,  indeed,  acquire  a  parallel  fibrous, 
or  even  bedded,  structure  by  flow  while  in  a  molten  state;  and 
some  geologists  maintain  that  the  bedded  structure  of  gneisses 
and  diorites  and  many  other  rocks  had  its  origin  in  the  flow  of 
molten  matter:  but  there  are  serious  objections  to  this  view.  We 
have  studied  them  without  any  theory  as  to  their  origin.  We  may 
admit  that  certain  rocks  which  we  have  grouped  with  the  sedi- 
mentary class  are  sometimes  eruptive,  or  that  certain  ones  have 
always  an  eruptive  origin.  If  so,  then  we  may  have  eruptive 
granites,  syenites,  diorites,  riorites,  and  diabases,  as  well  as  meta- 
morphic  ones  of  sedimentary  origin;  or  we  may  regard  some  of 
them,  like  diabase,  felsite,  and  the  porphyries,  as  exclusively 
eruptive.  In  any  event,  we  have  to  admit  the  existence  of  cer- 
tain rocks  which  bear  so  much  resemblance  to  modern  lavas  that 
we  can  regard  them  as  nothing  else  than  ancient  lavas. 

There  are  neither  modern  nor  ancient  lavas  lying  within  ac- 
cessible distance  of  us;  and  the  ancient  erupted  rocks  of  Lake 
Superior  and  the  Canadian  regions  have  not  endured  the  long 
journey  to  our  doors,  as  common  bowlders  have.  This  simple  fact 
gives  one  clew  to  their  nature.  They  are  more  basic;  they  con- 
tain mostly  less  silica,  at  least  they  are  not  quartzitic;  they  have 
dissolved;  they  have  been  worn  out.  So  much  is  certain.  But 
again,  we  have  learned  from  the  other  rocks  what  the  chemi- 
cal elements  are,  and  what  are  their  mineral  compounds.  The 
erupted  rocks  could  contain  few,  if  any,  new  minerals.  But, 
having  been  molten,  the  same  minerals  must  exist  in  a  blended 
condition.  Now,  though  it  is  impracticable  to  make  a  detailed 
study  of  the  eruptive  rocks,  we  may  report  that  investigation 
confirms  the  deductions  we  have  drawn.  So  we  have  chiefly  a 
feldspathic  series,  a  hornblendic  series,  and  an  augitic  series. 
Beyond  this  it  would  hardly  be  profitable  to  go  without  other 
facilities  than  we  propose  to  employ. 

The  following  rocks,  already  noticed,  are  included  also  among 
erupted  rocks:  granite,  granulite,  felsite,  syenite,  quartz-syenite, 


72  GEOLOGICAL   STUDIES. 

diorite,  quartz-diorite.  The  following  are  named  only  among 
eruptive  rocks:  1.  Feldspathic:  phonolite,  trachyte,  rhyolite  or 
glassy  rocks,  as  pearlstone,  pitchstone,  obsidian,  pumice.  2. 
Hornblendic  and  augitic:  andesite,  quartz-andesite  (dacite),  va- 
riolite,  augite-andesite,  dolerite  (basalt),  amphigenite  (Vesuvian 
lava).  On  "volcanoes"  and  "ancient  lavas"  see  Studies  XXIII 
and  XXIV. 

EXERCISES. 

What  is  the  material  of  our  so  called  lead  pencils?  What  proportion -of 
carbon  is  in  them?  How  does  graphite  differ  from  anthracite?  Is  graphite 
combustible?  What  gem  is  pure  carbon?  What  is  its  hardness?  Name  an- 
other carbonaceous  substance  with  much  lower  hardness.  How  does  peat 
differ  from  bituminous  coal?  From  what  is  peat  derived,  according  to  your 
observation?  What  is  paraffine?  What  are  its  uses?  In  what  respect  is 
amber  like  asphalt?  Have  you  ever  seen  a  magnetite  schist?  What  is  the 
color  of  the  dust  resulting  from  the  handling  of  magnetite  schist?  What 
color  of  dust  arises  from  haematite  schist?  What  color  of  dust  stains  the 
wagons  and  cars  carrying  Salisbury  (Conn.)  iron  ore?  What  color  of  dust 
stains  the  docks  at  Escanaba  and  Marquette,  Mich. ?  What  is  "cold  short " 
iron?  What  ore  of  iron  most  disturbs  the  magnetic  needle?  Name  the 
rocks  found  in  both  the  metamorphic  and  eruptive  series.  How  can  you  de- 
termine to  which  series  a  particular  granite  belongs? 


STUDY  XIV.— Retrospect  of  the  Rocks. 

A  retrospective  glance  over  the  rocks  which  are  here  studied 
recalls  the  fact  that  different  rocks  having  the  same  constituent 
minerals  differ  chiefly  in  their  structure.  They  may  be  crystal- 
line or  fragmental.  They  may  be  unstratified,  or  thick-bedded,  or 
thin-bedded.  They  may  be  well  consolidated,  or  imperfectly  so, 
or  quite  unconsolidated.  We  notice  that  most  of  the  rocks  are 
characterized  in  part  by  some  predominant  mineral,  such  as  quartz, 
mica,  hornblende,  pyroxene,  and  so  on;  and  that  we  thus  have 
several  series,  each  of  which  runs  through  the  various  types  of 
structure.  A  panoramic  presentation  of  the  common  rocks,  ar- 
ranged according  to  structure  in  the  several  series,  will  aid  greatly 


RETROSPECT   OF   THE   ROCKS.  73 

toward  a  comprehensive  grasp  of  the  subject.  Such  a  presenta- 
tion is  attempted  in  the  "  Table  of  Rock  Structure,"  which  fol- 
lows. 

Again,  we  may  make  an  arrangement  of  rocks  according  to 
the  minerals  which  they  contain,  noting  at  the  same  time  the  va- 
riations of  structure  for  the  same  mineral  aggregates.  This  is 
attempted  for  the  common  rocks  in  the  appended  "Table  of  Rock 
Composition."  In  this,  in  each  compartment,  the  "  massive " 
rock  stands  first,  and  is  put  in  small  capitals;  the  thick-bedded 
rock  next,  in  "Roman  letters";  and  the  thin-bedded  (to  which 
we  restrict  the  term  schist)  stands  last,  in  "  italics." 

Finally,  we  introduce  a  "Table  for  Rock  Determination," 
similar  to  our  previous  "  Table  for  Mineral  Determination."  The 
intention  of  this  is  to  enable  the  student  to  ascertain  the  name 
of  a  rock  as  soon  as  he  knows  its  constituent  minerals.  This 
table,  as  we  think,  will  be  found  extremely  useful;  and  much  ex- 
ercise should  be  had  on  it.  But  we  ought  to  remark  that  both 
the  tables  for  determination  contain  much  more  detail  than  the 
student  of  the  elements  of  geology  can  be  expected  to  acquire. 
Accordingly,  a  star  is  prefixed  to  names  of  species  regarded  im- 
portant for  the  elementary  student.  The  further  use  of  these 
tables  is  intended  for  more  advanced  study. 


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76 


GEOLOGICAL   STUDIES. 


TABLE  FOR  ROCK  DETERMINATION. 


L.  Crystalline— some  of  the  cpnstituent  minerals  having  shin- 
ing, lustrous  surfaces;  or  the  rock  is  fine,  compact 
and  hard. 

I.  PHANEROCRYSTALLINE,  consisting  of  minerals  distinguish- 
able with  naked  eye  or  pocket  lens. 

1.  QUARTZ  the  essential  constituent  of  the  rock. 
(1)  Massive  or  thick-bedded  (QUARTZITE). 

(a)  Composed  of  fragments  compacted  but  distinct, 
(aa)  The  constituents  are  rounded  pebbles, 
(66)  The  constituents  are  email  grains, 
(6)  Composed  of  grains  completely  blended  or  nearly  so, 
(2>  Thin-  or  moderately  thin-bedded, 
(a)  Composed  of  separate  grains,- 

(6)  Composed  of  a  somewhat  vitreous,  silicious  mass, 

2.  FELDSPAR  alone  with  quartz. 

(1)  Structure  massive, 

(2)  Structure  schistose, 

3.  MICA  a  leading  constituent  of  the  rock. 

(1)  Quartz  alone  with  mica, 
(a)  Massive  or  thick-bedded, 

(6)  Thin-bedded,  arenaceous-granular, 

(2)  Feldspar  alone  with  mica, 

(3)  Feldspar  and  quartz  with  mica  —  either  muscovite  or  bio- 

tite,  or  both  together ;  texture  coarse  or  fine ;  the 
feldspar  whitish  or  reddish;  the  quartz  without 
cleavage  planes. 

(a)  The  feldspar  not  in  definite  crystals,  but  fragments, 
(aa)  Massive,  granular, 

(66)  Thick- bedded,  or  sometimes  thin-bedded, 
(ee)  Thin-bedded,  mostly  with  little  feldspar, 
(6)  The  feldspar    in   defined  crystals,  or    some  of  it  so; 
massive, 

4.  HTDROMICA  a  leading  constituent. 

(1)  Quartz  alone  with  the  hydromica. 
(a)  Massive  or  thick-bedded, 

(6)  Thin-bedded,  arenaceous-granular, 

(2)  Feldspar  alone  with  hydromica. 

(3)  Feldspar  and  quartz  with  hydromica;  texture  coarse  or 

fine;  the  feldspar  mostly  whitish  or   reddish,  ex- 
hibiting cleavage  planes;  the  quartz  without  cleav- 
age planes, 
(a)  Massive  granular, 

(6)  Thick-bedded  and  sometimes  thin-bedded, 
(c)  Thin-bedded,  mostly  with  little  feldspar, 
(aa)  In  conspicuous  grains, 

(66)  Fine,  with  greasy  feel  (many   former  "  talcose " 
schists), 


Quartzose  Conglomerate. 
Granular  Quartzite. 
Vitreous  Quartzite. 

Quartzose  Schist. 
(  Silicious  Schist. 
j Jasper  Schist. 

Granulite. 
i  Granulite  Gneiss. 
i  Granulite  Schist. 


Micaceoua  Quartzite. 

Micaceous  Sandstone. 

Ninette. 


Granite  proper. 

Gneiss  proper. 

Mica  Schist. 

Porphyritic  Granite. 


Hydromica  Quartzite. 
Hydromica  Sandstone. 
Hydromica  Ninette. 


Hydromica  Granite. 
Hydromica  Gneiss. 

Hydromica  Schist. 
Sencite  Schist. 


RETROSPECT    OF   THE    ROCKS. 


77 


5.  AMPHIBOLE  a  leading  constituent. 

(1)  The   amphibole  occurring    as  hornblende  (commonest 

case). 

(a)  Hornblende  alone  present,  Amphibolite  or  Hornblende  Rock. 

(6)  Orthoclase  alone  present  with  hornblende,  Hyposyenite. 

(c)  Orthoclase  and  quartz  present,  with  often  some  biotite. 

(aa)  Massive,  Syenite  proper. 

(66)  Thick-bedded,  rarely  thin- bedded,  Syenite  Gneiss, 

(cc)  Thin-bedded  with  little  orthoclase,  Hornblende  Schist. 

(d)  Plagioclase  alone  present  with  hornblende. 

(aa)  The  plagioclase  acidic,  associated  often  with  some 
quartz  or  muscovite ;  color  grayish-white  to  green- 
ish, or  olive  green. 

(aaa)  Massive,  Diorite. 

(666)  Thick-bedded,  Diorite  Gneiss, 

(ccc)  Thin-bedded,  Diorite  Schist. 

(66)  The  plagioclase  basic,  generally  labradorite,  associ- 
ated with  biotite  and  no  quartz ;  texture  coarse  or 
fine ;  structure  massive  or  thick-bedded,  Norite,  part. 

(2)  The  amphibole  occurring  as  actinolite. 

(a)  Massive  and  tough,  Actinolite  Rock. 

(6)  Thin-bedded,  with  some  quartz,  Actinolite  Schist. 

(3)  The  amphibole  occurring  as  smaragdite  (a  light  green 

hornblende)  with  a  white  or  whitish  labradorite  in 

fine  grains  mottling  the  light  green  mass,  Euphotide. 

6.  PYROXENE  a  leading  constituent. 

(1)  Pyroxene  alone  present,  in  the  form  of  augite,  coarse  or 

fine  granular,  Pyroxenite. 

(2)  Orthoclase  present  abundantly  with  little  augite,  Augite  Hyposyenite. 

(3)  Plagioclase    present   with   pyroxene   (augite);     texture 

granitoid  or  fine. 

(a)  The  plagioclase  acidic,  ordinarily  oligoclaee,  Diabase,  part. 

(6)  The  plagioclase  basic. 

(aa)  The  pyroxene  lamellar  (diallagic) ;  the  plagioclase 
a  cleavable  labradorite;  texture  granular,  color 
reddish  to  dark  gray  and  grayish  black  (Gabbro 

of  some),  Norite,  part. 

(66)  The  pyroxene  granular;  the  plagioclase  anorthite 

or  labradorite ;  texture  fine,  Diabase,  part. 

(4>  Quartz  present  abundantly,  with  sahlite  and  some  feld- 

spar,  Pyroxene  Schist. 

7.  HYPERSTHENE  a  leading  constituent,  generally  with  cleav- 

able labradorite  [physically  like  Norite,   and  by 

some  so  called],  Hypersthenite. 

8.  EPIDOTE  the  characterizing  constituent. 

(1)  Epidote  alone,  or  nearly  so;  texture  fine  granular;  very 

hard ;  pale  green,  Epidote  Rock. 

(2)  Epidote  with  quartz  and  feldspar,  Unakite. 

9.  HYDROUS-M  AGNES  IAN  minerals  in  characteristic  abundance. 

(1)  Talc  alone  present,  in  a  massive  amorphous  state,  Steatite. 

(2)  Talc  with  quartz  and  feldspar. 


78 


GEOLOGICAL   STUDIES. 


(a)  Massive,  Protogine. 

(b)  Thick-bedded,  Protogine  Gneiss. 

(c)  Thin-bedded,  with  little  feldspar. 

(aa)  The  quartz  granular,  Talcose  Gneiss,  Protogine  Schist. 

(bb)  The  quartz  fine  and  nearly  wanting,  the  rock  mostly 

a  mass  of  minute  folia  of  talc,  Talcose  Schist. 

(3)  The  magnesian  mineral  is  chlorite ;  quartz  and  feldspar 

also  present. 

(a)  The  feldspar  abundant ;  structure  thick-bedded,  Chlorite  Gneiss. 

(b)  The  feldspar  scanty;  structure  thin-bedded,  Chlorite  Schist. 

(c)  The  feldspar  not  discernible ;  texture  very  fine,  struc- 

ture slaty,  Chlorite  Slate. 

(4)  The  magnesian  mineral  is  serpentine. 

(a)  Color  homogeneous  dark  green  to  greenish-black,  Serpentine. 

(b)  Color  mottled,  greenish  and  white,  being  mixed  with 

limestone  (" verd  antique"),  Ophiolite. 

10.  ALUMINOUS  minerals  in  characteristic  abundance. 

(1)  The  characterizing  mineral  pyrophyllite ;  color  white, 

gray,  or  greenish- white;  feel  greasy;   appearance 

that  of  a  talc  rock,  Pyrophyllite  Schist. 

(2)  The  characterizing  ingredient  argillaceous,  firmly  indu- 

rated, cleaving  into  thin,  even  layers  [Clay  slate, 

Phyllite],  Argillite. 

11.  CALCAREOUS  rocks;  hardness  not  above  3. 

(1)  Effervescence  with  dilute  acid  when  pulverized. 

(a)  Effervescence  with  cold  acid. 

(aa)  Rock  chiefly  calcareous,  Marble, 

(bb)  Rock  a  variegated  mixture  with  serpentine,  Ophiolite. 

(b)  Effervescence  only  when  heated,  Dolomitic  Marble. 

(2)  No  effervescence ;  hardness  about  2,  Gypsum. 

12.  CARBON  the  characterizing  constituent;   color  black  or 

dark-brown. 

(1)  Rock  distinctly  stratified;  hardness  2-2.5;  lustre  bright, 

often  sub-metallic;  iron  black  and  frequently 
iridescent;  fracture  conchoidal ;  burns  with  a  fee- 
ble flame  of  pale  color,  Anthracite. 

(2)  Rock  unstratified. 

(a)  Lustre  resinous ;  burns  freely,  Asphaltic  Substances. 

(b)  Lustre  metallic ;  streak  black  and  shining ;  color  iron 

black  to  dark  steel  gray ;  feel  greasy,  Graphite. 

13.  IRON  the  characterizing  constituent ;  specific  gravity  3.6  to 

5.3. 

(1)  Streak  black;    specific  gravity,  when  pure,  4.9  to  5.2;          I  Magnetite  Schist. 

acts  on  the  magnet,  '  Titanic  Iron. 

(2)  Streak  red;  specific  gravity,  when  pure,  4.5  to  5.3,  Haematite  Schist. 

(3)  Streak  dark  reddish  brown ;  acts  slightly  on  the  magnet ; 

contains  zinc,  Franklinite  Schist. 

(4)  Streak  brownish  yellow;  specific  gravity,  when  pure,  3.6 

to  4,  Limonite  Schist. 

(5)  Streak  white;   sp.  gr.  of  siderite  3.6  to  4.5;   effervesces 

with  hot  acid,  Spathic  lion. 


RETROSPECT    OF   THE    ROCKS. 


79 


II.    MICROCRYSTALLINE  and  CRYPTOCRYSTALLINE  rocks— sepa- 
rate crystals  or  grains  not  discernible  with  a  lens. 

A.  Texture  felsitic— partly  microcrystalline,  distinct  miner- 

als discernible  only  under  high  powers  in  thin  sec- 
tions. 

1.  Structure  massive  or  indistinctly  stratified. 

(1)  Color  black  or  nearly  black,  sometimes  greenish. 

(a)  Massive  or  thick-bedded,  Aphanite. 

(6)  Thin- bedded,  but  obscurely  so,  compact.  Aphanitic  Schist. 

(2)  Color  whitish,  reddish,  or  mottled. 

(a)  Essentially  orthoclastic  (see   page  27);   silica  inti- 
mately united;  hardness  quartz-like. 

(aa)  Without  imbedded  crystals;  color  mostly  red,  Petrosilex. 

(66)  With  imbedded  crystals  (or  alternating  bands)  of 

quartz  [Quartz  Porphyry],  Quartz  Petrosilex. 

(co  With  imbedded  crystals  of  feldspar,  Porphyritic  Petrosilex. 

(dd)  With  imbedded  pebbles,  Conglomerate  Petrosilex. 

(6)  Essentially   plagioclastic,  basic;   hardness  between 

feldspar  and  quartz. 

(aa)  Without  imbedded  crystals,  Felsite  proper. 

(66)  With  imbedded  crystals  (or  alternating  bands)  of 

quartz,  Quartz  Porphyry. 

(cc)  With  imbedded  crystals  of  feldspar    [Porphyry],       Porphyritic  Felsite. 

(c)  Essentially  quartzose ;  felsitic  texture  not  perfect,  Jasper  Hock. 

2.  Structure  distinctly  bedded  or  even  slaty,  Felsite  Schist. 

B.  Texture  colloid;  lustre  glassy;  constituent  minerals  com- 

pletely blended  or  nearly  so,  Rhyolite,  etc. 

C.  Texture  glassy,  lustre  quite  glassy;   translucent  or  trans- 


parent; colorless  or  white, 


Vitreous  Quartzite,  part. 


B.    Uncrystalline — fragmental    or    calcareous;      distinctly 
stratified. 

I.  Effervescence   with    acids,   at   least  when   pulverized    and 

heated. 

1.  Effervescence   with   cold    acids;    rock   sometimes    semi- 

crystalline,  sometimes  with  an  earthy  lustre. 

(1)  Well  consolidated,  Limestone. 

(2)  Partially  consolidated,  white  or  rusty,  Chalk. 

(3)  Unconsolidated,  putty-like  when  wet;  white,  Marl. 

2.  Effervescence  only  when  heated. 

(1)  Having  the  aspect  of  a  limestone;  of  ten  finely  granular,  Dolomite. 

(2)  Aspect  dark  and  earthy;  often  nodular,  Spathic  Iron. 

II.  No  effervescence  with  acids,  or  only  very  little. 

1.  Quartz  the  predominating  mineral. 

(1)  The  quartz  fragments  cemented  together. 

(a)  The  fragments  consist  of  rounded  pebbles,  Conglomerate. 

(6)  The  fragments  consist  of  fine  grains,  Sandstone. 

(2)  The  quartz  fragments  uncemented,  Sand. 

2.  Clay  the  predominating  ingredient. 

(i)  The  clayey  ingredient  somewhat  indurated,  but  the  rock 

fragile  and  breaking  into  thin  layers,  Shale. 


80 


GEOLOGICAL   STUDIES. 


(2)  The  clayey  ingredient  not  indurated, 
(a)  Mixed  with  various  impurities;    blue,  red,   dark,   or 

white, 
(6)  In  a  state  of  purity;  color  white, 

3.  Carbon  the  characterizing  constituent;  color  black  or  dark- 

brown. 

(1)  Rock  distinctly  stratified. 

(a)  Lustre  bright,  often  submetallic,  iron-black  and  fre- 
quently iridescent;  fracture  couchoidal;  burns  with 
a  feeble  flame  of  pale  color;  hardness  2  to  2.5, 

(6)  Lustre  pitchy;   fragile;   hardness  2  or  less;  burning 
with  a  yellow,  smoking  flame ;  surfaces  often  show- 
ing vegetable  structure  [Bituminous  Coals], 
(aa)  Softens  and  becomes  pasty  in  the  fire;  has  property 

of  caking, 

(bb)  Burns    freely  without  softening;    has    no   caking 
property, 

(c)  Lustre  dull;  color  generally  brownish  [Lignite], 

(2)  Rock  indistinctly  or  distinctly  stratified,  with  little  or  no 

lustre;  highly  bituminous, 

(3)  Rock  unstratified. 

(a)  Lustre  resinous;  burns  freely, 

(6)  Lustre  metallic ;  streak  black  and  shining;  color  iron- 
black  to  dark  steel  gray;  feel  greasy, 

4.  Iron  the  characterizing  constituent  (1),  (3)  and  (5)  gener- 

ally crystalline). 

(1)  Powder  black;  sometimes  as  black  shore-sand, 

(2)  Powder  red;  lustre  earthy;  consolidated  or  pulverulent 

[Red  Chalk,  Red  Ochre], 

(3)  Powder  dark  reddish  brown ;  contains  zinc, 

(4)  Powder  brownish  yellow ;  partially  consolidated,  granu- 

lar or  pulverulent  [Bog  Ore,  Shot  Ore,  Yellow  Ochre], 

(5)  Powder  white;  effervesces  with  acids  when  heated, 


Clay. 
Kaolin. 


Anthracite. 


Caking  Coal. 

Non- Caking  Coal. 
Brown  Coal. 

Cannel  Coal. 

Asphaltic  Substances. 

Graphite. 


j  Magnetic  Iron  Ore. 
\  Titanic  Iron. 


Hcematitic  Iron  Ore. 
Franklinite  Ore. 

Limonitic  Iron  Ore. 
Spathic  Iron. 


STUDY  XV.— Sedimentation. 


Let  us  visit  a  spot  overflowed  by  the  last  freshet.  We  go 
down  to  the  border  of  the  creek  and  find  the  flat  grimy  with  the 
muddy  slime  deposited  while  the  stream  was  out  of  its  banks. 
The  level  meadow  was  quite  covered  by  the  water;  and  we  can 
understand  that  many  overflows  must  make  material  additions  to 
the  land.  Indeed,  the  character  of  the  soil  here,  and  its  very 
level  surface,  show  that  during  times  past  this  piece  of  ground 
must  have  been  formed  from  sediments  deposited  at  times  of 


SEDIMENTATION. 


81 


overflow.  Deposits  from  rivers  are  called  Jluviatile,  and  the  land 
resulting  is  alluvial.  In  Cincinnati  at  the  time  of  great  floods, 
the  Ohio  River,  which  then  abounds  in  sediments,  leaves  a  thick 
layer  of  fine  sticky  mud  wherever  the  water  stands  —  in  streets, 
yards,  cellars  and  the  floors  of  first  stories  of  the  houses.  Think 
of  the  enormous  amount  of  mud  which  is  thrown  down  along  the 
whole  course  of  the  river  wherever  the  overflow  takes  place.  So 
the  river  becomes  bordered  by  alluvial  bottoms,  except  where  the 
banks  are  too  high  for  overflow.  The  same  is  true  of  the  Con- 
necticut, the  Potomac,  and  all  other  rivers. 

Let  us  go  down  by  the  pond;  here  we  shall  see  other  results 
of  the  process  of  sedimenta'tion.     Perhaps  this  pond  is  caused  by 


FIG.  25.— THE  LAKELET  SLOWLY  FILLING.    PBOCESS  or  SEDIMENTATION. 

a  dam  thrown  across  the  stream.  If  so,  your  father  or  uncle  may 
remember  when  the  dam  was  first  built;  it  was  not  a  century,  but 
notice  how  the  pond  is  "silted  up";  it  is  half  filled  with  mud  and 
sand  washed  in  from  the  adjacent  hill-slopes.  Perhaps  this  pond 
is  a  little  lake,  with  or  without  a  slight  outlet.  You  have  seen 
many  of  them.  They  abound  especially  in  our  New  England  and 
Northern  States.  Suppose  ourselves  standing  by  one  of  these 
lakelets.  It  looks  a  little  like  the  view  in  Fig.  25.  The  lakelet 
is  bounded  on  most  sides  by  elevated  ground,  but  on  one  side 
the  shore  is  low  and  marshy.  The  land  stretches  off  several  rods 
in  a  perfectly  level  marsh  or  meadow;  then  we  suddenly  reach 
the  firm  upland.  Down  by  the  water  the  marsh  grows  less  and 


82  GEOLOGICAL   STUDIES. 

less  firm.  Even  beyond  the  border  of  the  water,  some  sedges 
find  a  situation  suited  to  their  natures,  and  still  beyond,  bulrushes 
and  flags  rise  from  water  a  foot  or  more  in  depth.  On  other 
sides,  the  nature  of  the  lakelet  border  is  very  different.  Now 
consider  on  which  side  the  marshy  border  lies.  It  is  almost  al- 
ways on  the  side  opposite  that  from  which  the  prevailing  wind 
blows;  that  is,  it  is  the  easterly  side — ranging  from  northeast 
to  southeast.  The  leaves,  grasses  and  twigs  which  float  on  the 
water  surface  are  drifted  by  the  winds  toward  the  marsh,  where 
they  become  lodged  and  go  to  decay.  The  resulting  vegetable 
matter  forms  a  dark,  peaty  layer  on  the  bottom,  which  accumu- 
lates from  year  to  year.  It  stretches  from  the  land  down  and 
under  the  water.  As  the  land  grows,  the  marsh-grasses  and 
sedges  extend  their  area,  and  water-loving  plants  spring  from  the 
submerged  portion  of  the  peat.  Thus,  from  year  to  year,  the 
peat  extends  further  along  the  bottom,  and  the  land  encroaches 
upon  the  lake.  But  suppose  this  process  has  been  going  on  a 
thousand  years;  the  land  must  have  grown  lake  ward  quite  exten- 
sively. Indeed  it  has;  and  this  level  marsh  or  meadow  shows 
how  much  land  has  been  made  in  this  way.  Let  us  dig  in  this 
marsh.  You  know  beforehand  it  is  formed  of  black  "muck." 
And  now  we  see  why  the  marsh  is  exactly  level,  and  why  it  lies 
but  very  little  above  the  surface  of  the  water. 

But  here  is  another  phenomenon.  Underneath  the  inuck  or 
peat  is  a  bed  of  marl;  how  came  that  there?  Well,  going  down 
to  the  lakelet  again,  you  see  marl  lying  on  the  bottom;  so  of 
course,  as  the  peat  bed  extends,  it  covers  the  layer  of  marl.  An 
examination  of  the  marl  shows  numerous  dead  shells  —  uni- 
valves or  water  snails,  and  bivalves  or  mussels.  These  are  in  all 
stages  of  decay,  and  it  is  evident  that  much  of  the  marl  thus 
originates.  Living  snails  and  mussels  still  abound  in  the  water, 
especially  near  the  shores,  crawling*  on  the  bottom.  But  proba- 
bly some  portion  of  the  marl  results  from  precipitation  of  calcium 
carbonate  from  spring  waters,  as  briefly  explained  in  Studies  II 
and  XII. 

If  sediments  are  thus  accumulating  on  the  bottom  from  the 


SEDIMENTATION. 


83 


deposit  of  calcareous  matter,  and  from  the  wash  of  the  land; 
and  if  the  peat  marsh  is  gradually  encroaching,  what  must  be  the 
final  result?  Evidently,  the  lake  must  be  filled,  and  a  bed  of  peat 
underlaid  by  marl  will  occupy  its  place.  Now  you  understand 
the  origin  of  those  numerous  swales  and  bogs  and  tamarac 
swamps  which  exist  in  some  regions.  They  are  the  sites  of 
ancient  lakes.  Some  of  them  have  become  sufficiently  drained 
to  be  meadows,  or  even  arable  grounds.  The  old  swamps,  when 
thus  dried,  furnish  our  most  productive  lands,  because  they  are 
filled  with  the  very  materials  which  supply  the  chief  food  for 
vegetation. 

The  growing  swamp  is  not  always  on  the  lee  side  of  the  lake; 
it  will  be  found,  however,  on  the  side  toward  which  surface  mo- 
tion sets.  Sometimes  the  position  of  contiguous  hills  deflects 
the  prevailing  winds  from  their  normal  direction;  and  sometimes 
a  surface  drift  is  imparted  by  the  drainage  of  the  lakelet. 

We  must  study  a  little  farther  the  results  of  river  sedimenta- 
tion. Look  on  a  map  of  the  Mississippi  valley  from  Cairo  to  the 
Gulf  of  Mexico.  The  region  presents  but  a  very  gentle  slope, 
and  the  course  of  the  river  is  wonderfully  sinuous. 
For  the  whole  distance,  one  looks  out  from  the 
deck  of  a  steamboat,  over  a  wide  alluvial  plain, 
bounded,  at  a  greater  or  less  distance  from  the 
river,  by  high  banks.  Toward  the  gulf  it  expands 
in  a  triangular  form,  and  that  part  is  called  the 
delta.  Freqently  the  whole  alluvial  plain  is  so 
called.  This  plain  is  flooded  by  the  high  water 
of  certain  seasons  —  unless  confined  by  a  system  of 
embankments.  During  overflows  the  sediments 
subside  —  the  coarser  first  and  the  finer  afterward. 
This  is  familiarly  illustrated  by  the  subsidence 
which  takes  place  in  a  glass  of  water  as  shown  in 
Fig.  26.  We  may  suppose  this  is  a  glass  of  Mis- 
sissippi River  water  with  a  little  gravel  added. 

The  alluvial  deposit  of  the  Mississippi  has  thus  accumulated 
to  the  depth  of  ten,  twenty,  or  even  fifty  feet.  In  Fig.  27  we 


FIG.  26. 

ASSORTMENT 

or  SEDIMENTS 

IN  TURBID 

WATBR. 


84 


GEOLOGICAL   STUDIES. 


FIG.  27.— WINDINGS  OF  THE  MISSISSIPPI  FROM  VICKSBURG  TO  BATON  ROUGE. 


SEDIMENTATION.  85 

present  a  map  of  a  section  of  the  river  between  Vicksburg  and 
Baton  Rouge,  with  shading  to  indicate  the  breadth  of  the  alluvial 
belt.  Through  this  belt,  with  its  wonderful  network  of  bayous  of 
sluggishly  moving  water,  the  channel  pursues  its  sinuous  course, 
frequently  striking  the  high  upland,  and  affording  sites  for  cities 
and  villages,  as  at  Vicksburg,  Natchez,  and  other  points.  It  will 
be  noticed  that  the  stream  repeatedly  doubles  on  itself,  forming- 
peninsulas.  At  many  points  it  has  completely  worn  the  isthmus 
across,  forming  islands,  and  pursuing  a  new  channel,  as  seen  be- 
low Fort  Adams.  At  other  points,  as  near  Grand  Gulf  and  Port 
Hudson,  the  entrances  to  the  old  channels  have  been  "silted  up," 
and  the  old  channels  then  remain  as  lakes.  Thus  Bruiri  Lake 
was  cut  off  before  the  river  was  known  to  navigators;  Lake  St. 
Joseph  before  1700,  when  the  river  was  shortened  twenty  miles; 
and  Palmyra  Lake  was  formed  by  the  Davis  cut-off,  Z>,  in  1867, 
reducing  nineteen  miles  to  one.  In  one  memorable  instance  this 
conversion  of  a  peninsula  into  an  island  was  effected  by  human 
agency.  Notice  the  position  of  Vicksburg  on  the  map,  Fig.  27. 
During  the  late  war,  in  1862-3,  a  canal  was  dug  across  the  U  at 
(7,  for  the  passage  of  the  federal  gunboats,  to  enable  them 
to  shun  the  batteries  erected  on  the  Vicksburg  bluffs.  This 
canal  has  now  become  the  main  channel  of  the  river,  and  the  old 
channel  remains  a  mere  bayou  of  nearly  still  water,  greatly  to 
the  detriment  of  the  trade  of  the  city.  Sediment  is  constantly 
accumulating  in  it.  Only  one  expedient  seems  practicable.  The 
Yazoo  river,  which  empties  into  the  Mississippi  a  few  miles  above 
the  city  (see  map),  may  be  dammed,  and  its  waters  conducted 
through  a  canal  into  the  Mississippi  at  the  bend  of  the  U  above 
the  city.  This  river  then  would  scour  out  the  bayou,  and  Vicks- 
burg would  stand  on  the  Yazoo,  two  miles  above  its  mouth. 

When  it  is  noted  that  this  enormous  alluvial  deposit  extends 
to  the  Gulf  of  Mexico,  we  gain  some  conception  of  the  volume  of 
sediments  transported  by  the  Mississippi.  At  its  mouth  the  cur- 
rent is  met  by  a  body  of  salt  water,  over  which  the  river  dis- 
charges itself.  Here  the  slackened  motion  results  in  the  deposi- 
tion of  a  vast  volume  of  sediment  known  as  the  "bar."  But 


86  GEOLOGICAL   STUDIES. 

another  and  finer  portion  of  the  sediment  is  borne  to  sea  and 
taken  up  by  the  normal  oceanic  currents,  which  carry  it  to  great 
distances  before  it  finally  settles  down  upon  the  ocean's  bottom. 
All  the  rivers  which  empty  into  the  sea  are  similarly  contrib- 
uting sediments  to  be  added  to  the  layer  accumulating  over  the 
bottom.  Thus  the  oceans  are  filling,  as  well  as  the  lakes;  and 
the  ocean  sediments  are  burying,  also,  the  remains  of  the  mol- 
luscs and  fishes  which  lived  in  the  water  above  their  final  burial 
place.  The  dredge  brings  up  samples  of  the  sediments  for  our 
inspection.  They  are  coarser  and  more  abundant  nearer  the 
shore,  as  we  should  expect;  and  the  continental  sediments  cease 
almost  entirely  before  the  great  abyss  is  reached.  In  the  zone, 
from  two  to  three  miles  in  depth,  we  find  a  pretty  uniform  layer 
of  a  white  marly  substence  known  as  "globigerina  ooze,"  from 
the  predominance  of  microscopic  shells  of  Globigerina,  a  genus 
of  Foraminifera,  of  which  more  will  be  learned  in  Part  II.  With 
these  are  numerous  fragments  of  other  organisms,  especially  of 
Pteropods.  This  substance  when  dried  presents  the  appearance 
of  white  chalk;  and  in  fact,  white  chalk  is  largely  composed  of 
similar  organisms.  At  greater  depths  the  admixtures  with  globi- 
gerina ooze  diminish  in  quantity.  At  the  greatest  depths  is 
found  a  layer  of  fine,  homogeneous  reddish-brown  clay,  composed 
of  silica,  alumina,  arid  oxide  of  iron.  This  is  supposed  to  be  a 
residuum  left  after  the  solution  of  Globigerina  and  Pteropod 
shells  by  some  peculiar  action  of  the  abyssal  sea  water. 

EXERCISES. 

How  does  moving  water  act  to  separate  the  finer  and  coarser  particles? 
In  a  stream  flowing  from  a  steep  ravine  to  a  plain,  what  portion  of  the 
transported  material  will  be  deposited  on  the  plain?  What  portion  along 
the  slope?  Why  this  assortment?  Why  is  the  upper  layer  of  sediment  from 
a  pool  of  turbid  water  finest?  Is  the  alluvial  deposit  from  the  Mississippi 
fine  or  coarse?  Why  is  this  so?  Describe  a  stream  which  would  deposit 
pebbles.  What  do  you  know  about  the  power  of  Alpine  torrents?  What 
effect  is  produced  on  rock  fragments  transported  by  water?  Has  water  itself 
any  power  to  wear  the  rocks?  In  what  two  ways  do  rocks  disappear  under 
the  action  of  water?  [See  Studies  II,  III,  and  XVI.]  In  a  mixture  of  fine 


EROSIONS.  87 

sand,  powder,  and  slime,  how  may  water  be  used  to  separate  them?  Can 
you  think  of  other  moving  waters  besides  streams  which  also  exert  an  assort- 
ing action?  What  movements  of  the  ocean  do  this?  Why  are  the  coarsest 
pebbles  nearest  the  beach?  Why  are  some  beaches  pebbly  and  others  sandy? 
To  what  depth  are  the  ocean  waters  stirred  by  winds  and  tides?  What  kind 
of  sediments  would  be  borne  to  the  greatest  depths?  Why  are  the  most 
projecting  points  of  the  coast  rocky?  Would  marine  animals  generally 
prefer  to  live  about  such  points?  Why  do  we  not  find  good  shells  along  a 
stony  coast?  Mention  some  marsh  which  resulted  from  the  filling  of  a  lake. 
Ask  some  of  the  old  citizens  if  they  know  any  lake  or  pond  which  has  been 
filled  by  sediments.  Would  you  be  surprised  to  find  shells  in  a  bed  of  dry 
peat?  What  is  filling  the  Gulf  of  Mexico?  What  is  getting  buried  by  the 
sediments?  Do  you  think  the  deposits  are  all  uniform,  or  are  they  arranged 
in  layers?  What  would  cause  a  coarse  layer?  What  a  fine  layer?  Have  all 
rivers  deltas?  What  might  prevent  a  river  from  having  a  delta?  Mention 
a  river  without  a  delta.  Mention  rivers  with  extensive  deltas. 


STUDY  XVI.—  Erosions. 

We  have  seen,  in  various  situations,  a  great  amount  of  turbid 
water.  Some  of  this  stands,  for  a  time,  almost  motionless  ;  some 
is  hurried  onward  by  running  streams,  and  some  is  moved  by 
winds  and  currents  in  lakes  and  seas.  But  in  all  situations,  sus- 
pended sediments  tend  to  settle,  and  will  eventually  settle,  unless 
the  agitation  of  the  water  is  too  great.  We  have  seen  that  some 
of  the  material  moved  by  waters  consists  of  pebbles  and  larger 
stones.  Some  consists  of  sand  in  a  coarser  or  finer  condition. 
But  all  is  nearly  of  the  nature  of  the  drift  materials  covering  gen- 
erally the  surface  of  the  land.  That  is,  transported  sediments  are 
nothing  but  fragments  of  rocky  formations,  broken  and  ground 
and  pulverized.  Let  us  try  and  trace  some  of  them  to  their 
sources. 

Here,  first,  is  the  slime  settled  in  a  pool  by  the  roadside.  It 
is  quite  evident  that  the  last  rain  washed  the  material  from  the 
roadway  and  the  fields.  On  this  declivity  a  more  powerful  cur- 
rent has  cut  a  deep  gully,  which  renders  the  highway  almost  im- 
passable, and  the  bowlders,  stones,  pebbles,  sand,  and  mud  are 


88 


GEOLOGICAL   STUDIES. 


strewn  in  order  along  by  the  fences,  and  across  the  flooded  fields. 
The  sediments  are  derived  from  the  drift.  Every  rain-storm 
transports  portions  of  the  drift  from  the  higher  to  the  lower  lev- 
els. Every  rain-storm  carries  some  of  the  soil  from  the  ploughed 
fields,  and  leaves  it  in  the  bottom  of  the  lake,  or  spread  over  the 
alluvial  flat. 

Let  us  go  to  the  rocky  gorge.  Here,  in  ordinary  weather,  is 
a  small  stream,  though  noisy  ;  and  it  seems  to  have  accomplished 
a  great  work.  Usually  the  water  is  clear,  and  seems  to  move  no 
material  from  its  place.  But  how  came  this  deep  ravine  into  ex- 
istence ?  It  is  the  work  of  erosion.  You  have  seen  the  clear 
brooklet  swollen  to  a  torrent.  At  such  time  it  rises  to  the  level 
of  the  crumbling  banks,  and  tears  out  stones  and  sand,  and  hurls 
them  down  to  the  foot  of  the  gorge.  The  finer  sediment  is  carried 

miles  beyond  into  the  gentler 
current  of  the  river,  or  the  stand- 
ing water  of  the  lake.  Sometimes 
the  banks  of  the  gorge  are  rocky, 
but  the  roaring  torrent  cuts  its 
way  through  them,  and  the  strata 
stand  in  nearly  vertical  walls  on 
either  side.  In  southern  New 
York,  at  many  localities,  are  such 
deep  ravines,  cut  through  sand- 
stones and  shales,  nearly  horizon- 
tal in  position.  We  give  you  in 
Figure  28  a  view  of  one  at  Wat- 
kins'  Glen,  at  the  head  of  Seneca 
Lake.  This  is  a  very  picturesque 
region,  much  frequented  by  tour- 
ists. Many  other  gorges  may  be 
seen  along  the  Genesee  River,  in 
its  course  to  Lake  Ontario.  Do 
FIG.  28.— VIEW  IN  THE  GORGE  AT  WAT-  not  fail  to  notice  the  gorge  and 
KINS'  GLEN,  N.  Y.  ("RAINBOW  the  faus  at  Rochester,  when  you 
FALLS''),  ILLUSTRATING  EROSION  '  J 

BY  WATER.  pass  over  the  Central  Railroad. 


EROSIONS.  89 

In  the  northwestern  states  are  other  examples  of  erosion  equally 
beautiful  and  impressive.  The  Wisconsin  River,  in  its  course  to 
the  Mississippi,  has  cut  a  deep  channel  through  a  friable  sand- 
stone, giving  rise  to  a  great  amount  of  charming  scenery. 
One  of  the  views  is  presented  in  Fig.  29.  The  student  of  geol- 
ogy is  greatly  favored  in  this  fact,  that  the  very  data  of  his 
science  are  the  most  interesting  features  of  the  earth's  surface. 
The  greatest  of  rivers,  the  Mississippi,  has  also  effected  erosions 


FIG.  29.— THE  u DALLES"  OP  THE  WISCONSIN,  SHOWING 
RIVER  EROSION. 

worthy  of  its  greatness,  though  unimposing,  it  must  be  confessed,  in 
comparison  with  another  river  whose  equal  greatness  belongs  to 
a  past  age  of  the  world.  Along  the  upper  Mississippi,  high  cliffs 
line  the  valley  most  of  the  way  (Fig.  30).  The  Niagara,  as  every- 
one knows,  has  excavated  a  gorge  which,  with  the  "falls,"  its 
instrument,  is  the  wonder  of  the  world.  We  shall  have  to  con- 
sider this  in  other  connections.  (See  Figs.  305  and  306.)  But 
the  most  stupendous  examples  of  river  erosion  are  found  in  the 
Far  West.  The  Colorado  has  cut  prodigious  canons  through  the 


90 


GEOLOGICAL   STUDIES. 


horizontal  strata  to  the  depth  of  four,  five  and  six  thousand  feet. 

Many  of  its  tributary  streams  have  excavated  similar  gorges.  Thus 

much  of  the  region  is  scarred 
and  scored  in  a  manner  which 
renders  it  almost  impassable. 
We  cannot  conveniently  visit 
this  region,  but  we  supply  in 
Fig.  31  a  perspective  view  of 
the  "  Grand  Canon  "  at  the  foot 
of  the  valley  of  the  Toroweap, 
and  of  some  of  the  contiguous 
country.  The  total  chasm  pre- 
sents itself  in  two  stories.  The 
walls  of  the  outer  canon  stand 
five  or  six  miles  apart,  and  about 
2,000  feet  high.  The  inner 
canon  is  4,000  feet  wide  and 
3,000  feet  deep.  At  the  bottom 
flows  the  diminished  river,  about 
300  feet  across.  The  rocky  beds 
which  outcrop  in  the  nearly  ver- 
tical walls  vary  in  colors  from 
brilliant  red  to  creamy  yellow- 


FIG.  30.— CLIFF  ON  THE  UPPER  MISSIS- 
SIPPI  NEAR    TREMPEALEAU,  Wis.,     ish  and  gray.     But  we  must  not 
ILLUSTRATING      RIVER      EROSION. 
(Chamberlin.) 


enter  here  into  any  detailed 
statements.  For  these  we  refer 
the  student  to  the  glowing  pages  of  Captain  Button's  descrip- 
tion in  "The  Tertiary  History  of  the  Grand  Canon  District," 
in  the  Report  of  the  United  States  Geological  Survey  for  1881. 

These  examples,  with  others  which  may  be  familiarly  known 
to  the  student,  illustrate  the  destructive  action  of  flowing  water 
in  all  parts  of  the  world.  Aggregating  the  effects  of  thousands 
of  years,  we  begin  to  understand  how  enormous  has  been  the 
transportation  of  sediment  into  the  sea  through  the  agency  of 
rivers,  and  how  vast  has  been  the  destruction  of  the  land.  If  we 
stand  by  any  lake  or  ocean  shore,  we  shall  witness  a  different 


EROSIONS. 


91 


92 


GEOLOGICAL   STUDIES. 


action  of  the  same  agent.  Historical  records  assure  us  of  vast 
wastage  of  the  land  on  many  an  exposed  coast ;  and  we  shall 
learn  hereafter  that  ocean  waters  have  in  other  ages  covered  ex- 
tensive areas  now  dry  land,  and  have  worn  down  the  surface  hun- 
dreds and  thousands  of  feet.  The  very  canon  just  mentioned  is 
cut  in  a  plateau  which  has  itself  been  lowered  by  erosion  to  the 
extent  of  10,000  feet;  and  this  plateau  occupies  an  area  of  13,000 
to  15,000  square  miles.  The  student  may  calculate  how  many 
cubic  yards  the  land  has  lost,  and  how  many  have  been  spread 
over  the  bottom  of  the  sea. 

The  evidences  of  the  great  wastage  of  the  land  in  times  past 
can  everywhere  be  seen.  Sometimes  extensive  masses  are  under- 
mined, and  tumble  down.  This  accelerates  their  final  disappear- 
ance (Fig.  32).  In  the  year  1248  a  large  part  of  a  mountain  in 

Savoy  fell  to  the  plain,  under  the 
action  of  frost.  The  mountain  rose 
4,000  feet  above  the  plain,  and  was 
capped  by  600  feet  of  limestone.  The 
undermining  of  this  mass  caused  the 
precipitation  of  sufficient  material  to 
cover  nine  square  miles  with  frag- 
ments, and  entirely  bury  five  parishes, 
together  with  the  town  and  church  of 
St.  Andre.  In  1751  a  series  of  ava- 
lanches fell  during  several  days  from 
a  mountain  near  Servos,  in  Savoy, 

which  sent  up  a  cloud  of  dust  visible  twenty-five  miles.  The 
amount  of  material  precipitated  was  15,000,000  cubic  feet.  Many 
similar  cases  could  be  cited. 

This  underminining  process  is  the  method  of  recession  of 
water-falls,  as  will  be  shown  hereafter  (Figs.  305  and  306). 

The  central  part  of  Tennessee — that  known  as  the  "central 
basin  "  —  is  a  vast  sunken  area  more  than  a  hundred  miles  in 
diameter  ;  and  this  has  evidently  been  produced  by  the  removal 
of  many  cubic  miles  of  rocky  material  through  some  process  of 
erosion  in  times  past.  All  around  the  border  of  this  basin  rise  the 


FIG.  32.  — MAGNESIAN  LIMESTONE 
UNDERMINED  BY  THE  DISINTE- 
GRATION OF  A  SANDSTONE  BE- 
NEATH. (Chamberlin.) 


EROSIONS. 


93 


rocky  walls  of  the  remaining  por- 
tions of  the  formations  a  hundred 
feet  high,  or  more.  In  East  Ten- 
nessee is  another  valley  formed  by 
extensive  erosion.  These  are  shown 
in  the  cut,  Fig.  33.  See  also  how 
the  nearly  vertical  strata  of  the 
Unaka  range  have  been  worn  down 
to  mere  stumps.  Where  have 
gone  the  continuations  of  these 
upturned  strata? 

We  direct  the  student's  atten- 
tion to  one  more  example.  In 
Fig.  34  is  shown  the  evidence  of 
vast  erosion  in  the  Appalachians. 
Here  the  actual  surface  is  shown 
along  ABC.  The  slight  eleva- 
tion at  A  represents  truly  one  of 
the  ranges  of  the  Allegheny 
Mountains.  B  represents  the  range 
known  as  Bald  Eagle  Mountain. 
Notice  the  foldings  of  the  vast 
series  of  strata.  Notice  the  moun- 
tain mass  represented  by  E,  which 
once  rose  35,000  feet  above  the 
present  surface,  and  all  has  been 
carried  away  by  erosion.  This 
section  is  in  Centre  County,  and 
shows  but  a  fraction  of  a  full  sec- 
tion across  the  Appalachian  chain. 
But  all  the  mountain  elevations 
have  been  similarly  worn  down. 

In  very  numerous  cases  singu- 
lar columns  of  the  eroded  rock 
have  escaped  erosion.  Sometimes, 
as  in  Monument  Park,  Colo- 


94 


GEOLOGICAL   STUDIES. 


FIG.  34.— ILLUSTRATING  ENORMOUS  EROSION  IN  THE  APPALACHIAN  REGION.  (After  Les- 
ley.) A,  Allegheny  Mountain  at  Snow  Shoe;  B,  Bald  Eagle  Mountain;  ABC,  present 
surface  — all  above  being  swept  away;  D,  probably  a  subterranean  mountain  of  Eozoic 
rocks ;  II  to  HI,  Cambrian ;  IV  to  VI,  Silurian ;  VII  to  IX,  Devonian ;  X  to  XII,  Lower 
Carboniferous;  XIII,  Coal  Measures.  Compare,  for  explanation,  Study  XVII. 


FIG.  35.— COLUMNS  IN  MONUMENT  PARK,  COLORADO.     (Hayden.) 


EROSIONS. 


95 


rado  (Fig.  35),  and  in  some  parts  of  Wisconsin  and  Minnesota, 
they  have  been  protected  by  a  fragment  of  harder  rock,  which 
rests  on  them  like  a  cap.  Sometimes,  as  in  the  Plateau  Province 
of  Colorado,  the  rock  masses  around  such  columns  have  been 
worn  away  by  streams  of  water. 

We  must  not  forget  that  mere  weathering  accomplishes  much. 
This  includes  the  mechanical  action  of  beating  rain,  hail,  and 
snow,  and  disintegrating  frost,  as  well  as  the  solvent  action  of 
water.  On  the  dome  of  St.  Paul's,  in  London,  the  more  rapid 
weathering  of  the  stone  causes  some  of  the  fossils  to  project  a 
quarter  of  an  inch,  as  before  stated.  This  observation,  made  in 
1873,  was  after  an  exposure  of  one  hundred  and  sixty-three  years. 
At  this  rate  7,824  years  would  be  required  for  the  wastage  of 
the  stone  to  exceed  that  of  the  fossil  to  the  extent  of  one  foot. 
As  the  fossil  itself  wasted  probably  half  as  rapidly  as  the  stone, 
we  may  safely  as- 
sume that  the  wast- 
age of  the  rock  was 
not  less  than  a  foot 
in  4,000  years. 

Many  instructive 
examples  of  atmos- 
pheric decay  may  be 
seen  among  granite 
rocks.  Here  (Fig. 
36)  is  a  view  of  the 
summit  of  Mt.  Hoff- 
man, Sierra  Nevada, 
showing  the  bowl- 
der-like forms  re- 
sulting from  atmos- 
pheric  action.  A 
more  striking  exam- 
ple is  shown  in  Fig. 

37,  where  one  of  the  granite  ridges  between  the  Temescal  and 
San  Bernardino  ranges,  in  California,  is  weathered  to  a  state 


FIG.  36. — SUMMIT  or  MT.  HOFFMAN,  SIERRA  NEVADA, 
SHOWING  DISINTEGRATION  OF  GRANITE.  (Photograph.) 


96 


GEOLOGICAL   STUDIES. 


which  presents  the  appearance  of  a  bowlder-strewn  surface.  The 
weathering  of  granite  is  peculiarly  apt  to  result  in  bowlder-like 
forms;  and  it  can  hardly  be  doubted  that  they  have  sometimes 
been  mistaken  for  true  glacial  bowlders,  even  in  tropical  countries. 
Much  attention  has  been  given  to  the  wastage  of  the  land 
generally.  Some  good  authorities  conclude  that  most  continental 
surfaces  are  lowered  by  erosion  not  less  than  a  foot  in  six  thou- 
sand years.  It  has  lately  been  calculated  by  T.  Mellard  Reade 
that  when  we  take  account,  also,  of  wastage  by  solution,  the  sur- 


FIG.  37.  —  A  RIDGE  OF  GRANITE  WITH  BOWLDER-LIKE  MASSES  RESULTING  FROM 
WEATHERING.     (Whitney.) 


face  of  the  basin  of  the  Mississippi  is  lowered  a  foot  in  four 
thousand  five  hundred  years;  and  that  one  hundred  tons  are 
removed  annually  from  every  square  mile  of  the  two  Americas. 
The  wastage  of  the  land  is  called  denudation. 

So  we  may  learn  that  there  has  been  vast  destruction  of  the 
rocks  during  the  course  of  many  ages.  They  have  been  gradually 
reduced  to  gravel  and  mud,  and  even  solutions,  and  carried  off 
by  the  streams,  to  be  laid  down  on  the  plains,  or  spread  as  sedi- 
ment, if  undissolved,  over  the  bottom  of  the  sea.  [For  other 
interesting  illustrations  of  erosion  see  Figs.  85,  86,  95,  55,  and  66.] 


STKATA,    AND    WHAT   THEY   TEACH.  97 


EXERCISES. 

From  what  are  sand  and  mud  derived?  Was  the  Mississippi  mud  ever 
in  a  rock  condition?  How  might  it  be  made  rocky  again?  Would  it  become 
chalk?  Could  it  be  made  a  granite?  What  agents  produce  sand  and  mud 
from  the  rocks?  How  does  frost  act?  How  does  a  stream  of  water  act? 
Mention  some  ravine  excavated  by  running, water.  Is  the  excavation  in 
drift  or  solid  rock?  Where  has  the  material  been  carried?  How  far  can  you 
trace  it  in  thought?  What  is  the  source  of  the  sediments  of  the  Mississippi? 
Which  is  most  turbid,  the  Upper  Mississippi  or  the  Missouri?  What  is  the 
cause  of  the  difference?  Whence  comes  the  mud  which  forms  the  bar  of  the 
Mississippi?  What  is  the  color  of  the  water  in  the  lower  Mississippi?  What 
is  the  color  of  the  water  in  the  bayous  of  Louisiana  and  Mississippi?  Has 
the  Red  River  any  delta?  Would  the  erosions  of  the  Missouri  and  the 
streams  which  feed  it  have  any  tendency  to  lower  the  Rocky  Mountains? 
Where  are  the  sources  of  the  Ohio?  Does  New  York  state  contribute  any- 
thing to  the  bar  of  the  Mississippi?  What  is  the  effect  of  denudation  on  the 
depth  of  the  soil?  Are  the  soils  generally  disappearing?  In  what  situations 
are  soils  accumulating?  If  a  hundred  tons  of  material  disappear  annually 
from  every  square  mile,  to  what  extent  does  this  lower  the  surface?  [Calcu- 
late by  assuming  a  mean  specific  gravity  for  the  material.]  Why  do  bed  rocks 
project  above  the  soil  in  some  places  and  not  in  others?  Is  there  any  danger 
of  the  disappearance  of  the  soil  in  a  hilly  country?  Which  surface  lowers  most 
rapidly,  that  of  West  Virginia  or  that  of  northern  Illinois?  Can  you  think 
of  any  reason  why  the  plateaus  of  Colorado  and  Utah  are  more  denuded  than 
the  surface  of  Louisiana?  Suppose  the  stone  on  the  dome  of  St.  Paul's 
Cathedral  in  London  is  still  one  foot  thick,  how  thick  will  it  be  (on  the  data 
given)  one  thousand  years  from  now,  if  the  cathedral  is  still  standing? 


STUDY   XVII.— Strata,  and  What  They  Teach. 

Most  students  of  geology  have  been  at  some  time  in  a  stone 
quarry.  There  they  have  seen  the  quarrymen  drilling  and  blast- 
ing and  prying  to  remove  slabs  or  layers  of  the  rock.  Such  slabs 
are  used  in  the  stone  walls  of  houses,  sometimes  in  sidewalks, 
and  sometimes,  where  they  are  thin  layers  of  slate,  they  are  em- 
ployed in  roofing.  In  quarries  of  granite  or  other  crystalline 
rocks,  the  slabs  are  very  thick,  as  you  have  already  learned,  and 
the  stones  are  worked  out  in  large  cuboidal  blocks.  But  in  al- 


98  GEOLOGICAL   STUDIES. 

most  every  case  you  will  notice  that  the  rocks  in  the  quarry  lie  in 
layers,  thick  or  thin.  Each  layer  is  a  stratum,  and  two  or  more 
layers  are  called  strata.  We  often  also  call  them  beds.  If  you 
go  back  to  Watkins'  Glen,  Fig.  28,  you  perceive  that  the  strata 
are  quite  thin  or  slaty ',  or,  as  we  have  before  said,  thin-bedded. 
The  rocks  shown  in  Fig.  29  are  also  thin-bedded.  In  both  cases 
the  strata  are  nearly  horizontal.  Almost  everywhere  the  stratifi- 
cation or  bedding  of  the  rocks  can  be  detected.  We  must  try  to 
ascertain  how  the  bedded  structure  has  been  produced. 

You  have  seen  the  brooks  and  rivers  at  work  tearing  down 
the  land.  You  have  seen  the  waves  corroding  the  beach.  You 
have  thought  on  the  slow  disintegration  of  all  the  surface  rocks 
by  rains  and  frosts,  and  the  perpetual  wearing  of  the  loose  mate- 
rials of  the  drift;  and  you  have  seen  the  waters  carrying  away 
the  sediments  to  the  sea.  In  thought  you  have  followed  those 
sediments  in  their  distribution  over  the  ocean's  bottom.  You 
have  seen  them  lying  and  accumulating  there,  while  dead  shells 
and  bits  of  coral  and  bones  of  fishes  have  been  mingled  with  the 
growing  deposit.  What  appearance  must  the  sediments  present 
in  case  a  few  acres  of  sea  bottom  could  be  taken  out  bodily  and 
inspected?  The  sediments  would  consist  of  layers  parallel  with 
each  other.  They  would  be  distinguished  by  different  colors  and 
by  different  degrees  of  fineness.  Imbedded  in  the  substance  of 
the  layers  would  be  the  relics  of  the  animals  which  have  lived  in 
the  sea.  Is  this  a  correct  statement  of  what  you  would  see? 
Think  about  it.  The  depth  of  the  accumulated  sediments  would 
correspond  to  the  time  spent  in  their  accumulation.  You  might 
look  at  them  and  reflect:  "These  layers  of  mud  and  sand  were 
once  far  inland.  They  were  once  part  of  the  soil  of  cornfields 
and  gardens.  Crops  grew  on  them.  The  gully  in  the  road  was 
made  by  the  removal  of  them.  They  came  down  the  rivers. 
Some  started  on  the  slopes  of  distant  mountains.  The  Missouri 
brought  some  from  the  gorges  and  summits  of  the  Rocky  Moun- 
tains. Some  came  out  of  the  deep  and  gloomy  canons  of  the 
Colorado.  Some  came  from  the  storm-torn  bluffs  at  Long  Branch 


STRATA,    AXD   WHAT  THEY   TEACH.  99 

or  Coney  Island  or  Gay  Head.  Some  was  yielded  by  the  slowly 
dissolving  promontories  of  Nahant  and  Marblehead." 

That  is  what  you  might  think;  and  such  reflections  are  sug- 
gested by  our  observations  on  the  processes  of  erosion  and  sedi- 
mentation. Now  suppose  the  layers  of  sediments  pressed  by 
thousands  of  tons  of  weight.  The  deeper  ones  are  so  pressed  when 
many  feet  of  later  sediments  are  deposited  upon  them.  All  are 
so  pressed  by  the  mere  weight  of  deep  water.  They  would  thus 
be  condensed  into  a  solid  state  —  like  the  paper  pulp  which  is 
manufactured  into  car-wheels.  They  would  be  rocks.  The  rocks 
would  be  composed  of  strata.  The  thin  layers  would  be  laminae. 
The  shells  and  corals  pressed  in  the  rocks  would  be  fossils.  This 
is  almost  exactly  what  we  have  at  Watkins'  Glen,  and  in  the  ma- 
jority of  the  rocks  underlying  the  country.  All  our  limestones, 
sandstones  and  shales  were  once  just  such  sea  sediments.  The 
limestones,  however,  contain  a  very  large  proportion  of  matters 
contributed  by  the  decay  of  shell-bearing  animals. 

You  have  already  learned,  however,  that  many  rocks  do  not 
exhibit  so  distinct  evidences  of  stratification  as  may  be  seen  in 
ordinary  sandstones,  shales  and  limestones.  In  fact,  most  of  our 
bowlders  are  only  obscurely  stratified,  because  rocks  of  this  kind 
resist  destruction  more  successfully  than  the  rocks  more  distinctly 
stratified.  These  hard  or  crystalline  rocks  come  to  the  surface, 
or  outcrop,  in  most  parts  of  New  England  and  along  our  northern 
border.  But,  as  before  said,  they  are  really  stratified,  and  must 
be,  therefore,  of  sedimentary  origin  like  the  others.  They  have, 
therefore,  been  altered  since  they  existed  in  a  condition  similar  to 
the  others.  This  alteration  is  known  also  as  met amor phism.  The 
causes  of  it  have  been  much  studied;  birt  there  are  still  some 
mysteries  about  it.  We  understand,  however,  that  great  press- 
ure, great  heat,  and  chemical  operations  have  had  much  to  do 
with  metamorphism.  The  effect  of  it  is  to  render  a  rock  less  dis- 
tinctly stratified,  harder,  more  crystalline  and  less  clearly  fossilif- 
erous.  So  metamorphism  impresses  characters  which  are  easily 
observed. 

When  we  find  metamorphic  rocks  in  place,  that  is,  in  solid 


100  GEOLOGICAL   STUDIES. 

ledges  instead  of  bowlders  or  detached  fragments,  we  generally 
find  them  underlying  in  relative  position  all  the  non-metamor- 
phic  rocks.  This  is  plainly  seen  when  we  are  able  to  trace  them 
to  their  contact  with  other  rocks.  In  Fig.  38,  a,  granite,  and  b, 
gneiss,  are  metamorphic  or  crystalline,  and  c,  a  sandstone,  is  un- 
crystalline.  Now  if  we  start  from  the  highest  point  and  travel 
toward  the  sandstone,  we  find,  on  reaching  it,  that  it  overlies  the 
gneiss,  as  the  gneiss  overlies  the  granite.  Now  notice  that  the 
granite  and  gneiss  not  only  underlie  the  sandstone  at  the  point  of 
contact;  they  are  everywhere  stratigraphically  lower  than  the 
sandstone,  even  where  their  outcrops  are  topographically  higher 
than  the  sandstone.  This  frequent  arrangement  of  strata  in 
respect  to  positions  it  is  very  important  to  observe  and  under- 
stand. An  outcrop  of  one  stratum  at  a  higher  level  than  another 


b  a,  be 

FIG.  38. — CRYSTALLINE  AND  UNCRYSTALLINE  ROCKS. 

a,  Granite;  6,  Gneiss;  c,  Sandstone. 

does  not  indicate  whether  it  is  stratigraphically  higher  or  lower. 
We  must  take  particular  notice  of  the  dips  of  the  two  strata. 
The  dip  is  the  direction  in  which  they  incline  downward.  In  Fig. 
38  the  gneiss  and  the  sandstone  dip  in  the  same  direction;  but  as 
the  gneiss  has  the  greatest  dip  it  passes  under  the  sandstone. 
This  is  a  case  of  unconformability  —  the  two  dips  being  different. 
The  position  of  the  sea  bottom  was  different  when  the  gneiss 
materials  were  laid  down  from  its  position  when  the  sandstone 
materials  were  laid  down.  This  single  observation  shows  that 
the  sea  bottom  has  sometimes  undergone  a  tilting  or  inclination, 
and  that  afterward  later  sediments  have  been  laid  down. 

Look  again  at  Fig.  38.  Here  is  also  a  record  of  erosions. 
The  gneiss  on  one  side  of  the  granite  dips  in  a  direction  opposite 
to  the  dip  on  the  other  side.  Suppose  the  granite  could  be 
pushed  down  so  as  to  lower  the  gneiss  to  a  horizontal  position; 


STRATA,    AND    WHAT 

the  gneiss  of  the  two  sides  would  become  nearly  continuous, 
only  some  portion  would  be  wanting.  Now  we  may  fairly  assume 
that  the  anticlinal  position  (both  ways  dipping)  of  the  gneiss  has 
resulted  from  the  uprise  of  the  granite  from  beneath  the  for- 
merly horizontal  gneiss.  If  so,  the  gneiss  may  have  been  origi- 
nally continuous  over  the  summit  of  the  uplifted  granite,  and 
have  been  subsequently  removed  by  processes  of  erosion.  In 
such  case,  the  outcropping  extremities  of  the  gneiss  strata  are 
the  mere  stumps  of  a  wasted  formation,  and  have  been  brought 
to  a  position  higher  than  the  sandstone  by  an  uplift  subsequent 
to  the  deposition  of  the  gneiss  sediments.  We  might  reasonably 
conclude  that  there  has  been  another  uplift  since  the  deposition 
of  the  sandstones;  for  they  are  also  somewhat  tilted.  Thus  the 
steep  inclination  of  the  gneiss  may  be  the  result  of  two  or  more 
uplifts.  These  things  should  be  much  reflected  on. 

From  the  simple  stratigraphical  observations  thus  far  made, 
we  may  draw  inferences  like  the  following: 

1.  The  duration  represented  by  so  enormous  a  pile  of  sedi- 
ments as  have  come  to  our  knowledge,  must  have  been  vast. 

2.  The  sea  has  covered  all  the  land,  for  all  lands  are  under- 
laid by  sedimentary  rocks.     The  sea  was  once  universal. 

3.  Some  special  action  has  been  exerted  upon  the  sediments 
to  change  them  from  earthy  strata  into  crystalline  rocks. 

4.  The  land  has  resulted  from  an  upheaval  of  the  bottom  of 
the  sea;  and  upheavals  have  occurred  more  than  once  in  the 
same  region. 

5.  The  upheaval  of  the  sea  bottom  bent  and  fractured  the 
strata,  and  threw  them  into  inclinations  more  or  less  steep. 

6.  The  work   of  denudation  has  removed  the  upper  strata 
over  the  higher  summits,  and  left  the  strata  lower  in  geological 
position  to  stand  at  higher  elevations  than  strata  higher  in  geo- 
logical position. 

7.  The  movement  of  such  enormous  masses  of  rocks  implies 
the  exertion  of  force  inconceivably  great.     The  nature  of  this 
force  will  be  an  important  subject  for  future  study. 


GEOLOGICAL   STUDIES. 


EXERCISES. 

In  what  attitude  are  layers  of  sediments  originally  deposited?  How,, 
then,  do  we  find  them  almost  always  in  an  inclined  position  as  strata?  Did 
you  ever  notice  strata  standing  almost  on  edge?  Explain  how  this  could  be. 
Give  the  history  of  strata  whose  edges  come  up  to  the  surface  of  the  earth. 
Draw  a  diagram  showing  how  strata  older  in  age  may  appear  higher  topo- 
graphically. Draw  one  showing  how  newer  strata  may  appear  higher  topo- 
graphically. Draw  a  diagram  showing  conformability  of  strata.  Draw  one 
showing  unconformability  of  strata.  Suppose  we  have  several  strata,  of 
which  the  lower  is  composed  of  pebbles  and  the  others  are  progressively  finer, 
what  conditions  produced  this  result?  Suppose  we  can  trace  a  stratum  for 
many  miles,  and  find  it  graduating  from  a  conglomerate  to  a  coarse  sandstone, 
and  then  to  a  fine  one;  explain  this.  If  we  could  trace  it  further,  what  fur- 
ther change  might  be  expected?  In  what  direction  do  older  strata  dip  in 
reference  to  newer?  In  what  direction  do  newer  strata  dip  in  reference  to 
older?  Can  you  give  any  reason  why  metamorphic  rocks  are  generally  more 
deeply  seated  than  others? 


STUDY  XVIII.— Ifbssils,  and  What  They  Teach. 

Now,  once  more  let  us  carry  our  thoughts  back  to  the  bottom 
of  the  sea,  where  the  sediments  are  continually  burying  the  or- 
ganic relics  of  the  sea.  Relics  once  buried  become  buried  deeper 
and  deeper.  By  and  by  some  of  them  are  a  hundred,  or  even  a 
thousand,  feet  beneath  the  ocean  bed,  and  the  sediments  are  be- 
coming subjected  to  an  enormous  pressure,  and  are  hardening  into 
solid  strata.  Now,  the  amount  of  sediment  in  sea  water  far  from 
land  is  generally  small.  The  accumulation  of  successive  layers 
is,  therefore,  very  slow.  We  can  understand  that  when  they  have 
become  a  thousand  feet  deep  probably  many  thousands  of  years 
must  have  passed  by.  In  that  time  the  inhabitants  of  that  part 
of  the  ocean  may  have  changed  greatly.  The  water  is  now  a 
thousand  feet  shallower  than  it  was.  The  deep-water  species 
which  dwelt  there  at  first  have  migrated  to  a  region  where  the 
water  is  still  deep.  Shallow-water  species  are  here  now.  So  the 
remains  of  the  former  kind  are  imbedded  in  the  deep  sediments, 


FOSSILS,    AND    WHAT   THEY   TEACH.  103 

and  those  of  the  latter  kind  in  the  later  sediments.  But  the 
ocean  bottom  sometimes  changes  its  level.  If  it  has  been  sink- 
ing here,  the  depth  may  be  as  great  as  at  first;  but  if  it  has  been 
rising,  the  depth  is  diminished  even  more  than  is  due  to  the  ac- 
cumulation of  sediments.  Perhaps  the  nearest  land  has  been  more 
upraised,  and  the  shore  is  now  nearer  to  this  spot;  coarser  sedi- 
ments are  now  deposited  here;  the  mud-loving  populations  have 
emigrated,  and  this  place  is  taken  by  populations  which  like  a 
sandy  bottom.  If,  therefore,  we  could  examine  an  extensive 
series  of  strata,  we  should  find  them  distinguished  by  their  or- 
ganic contents,  as  well  as  by  their  constitution  and  color. 

Now  let  us  examine  such  a  series.  Every  high  rock  precipice 
presents  one;  every  deep  river  gorge  presents  one;  the  canons  of 
the  Colorado  present  magnificent  examples.  Let  us  put  different 
series  together,  so  that  we  may  inspect  a  continuous  series  from 
the  oldest  rocks  known  up  to  the  latest.  The  column  is,  say,  a 
hundred  thousand  feet  high  (see  this  in  Fig.  39).  What  is  shown? 
Something  even  more  instructive  than  would  have  been  antici- 
pated. The  lowest  rocks  are  granites,  and  gneisses,  and  crystal- 
line schists.  They  contain  no  fossils.  Either  there  was  no  life  in 
the  ocean  when  they  were  formed,  or  its  relics  have  been  oblit- 
erated by  metamorphism.  But  we  must  not  say  there  was  no 
life.  Very  rarely  some  obscure  traces  are  seen  in  some  of  the 
serpentinous  marbles  well  toward  the  bottom  of  the  series.  They 
are  extremely  simple  in  organization.  We  shall  study  them  here- 
after, and  learn  that  they  belong  to  the  sub-kingdom  of  proto- 
zoans—  the  simplest  of  all  animals.  Above  the  level  of  the 
crystalline  rocks  we  find  organic  remains  quite  abundant.  Some 
of  them  are  univalve  shells;  some  are  bivalves;  some  remind  us  of 
certain  crab-like  forms,  and  some  are  entirely  strange  and  curious. 
But  they  are  all  marine  invertebrates.  We  find  nothing  with  a 
backbone  ;  we  find  nothing  which  lived  on  the  land ;  we  find 
nothing  nearly  related  to  creatures  which  inhabit  fresh  water  in 
our  times. 

The  relics  of  marine  invertebrates  are  found  all  the  way  from 
this  level  to  the  top  of  the  series.     But  somewhat  further  up  we 


104  GEOLOGICAL   STUDIES. 

encounter  the  bones,  and  teeth,  and  armor  plates  of  fish-like  creat- 
ures. True,  they  are  not  much  like  the  remains  of  modern  fishes; 
but  we  call  them  fishes.  These  creatures  were  at  least  bone-bear- 
ing-, and  though  without  backbones,  they  had  something  corre- 
sponding to  the  backbone.  They  were  vertebrates  •  but  they 
were  marine  vertebrates,  if  we  may  judge  from  the  remains  of 
other  marine  animals  surrounding  them.  These  very  peculiar 
fishes  do  not  continue  to  the  top  of  our  series;  they  seem  to  have 
lived  only  during  a  certain  age  of  the  world.  (Compare  Fig.  39.) 

Next  we  come  to  a  zone  of  strata,  in  which  lie  the  vertebrae, 
skulls,  and  other  remains  of  creatures  related  to  our  frogs  and 
salamanders.  They  were  of  the  type  of  amphibians.  We  feel  jus- 
tified in  concluding  that  they  lived  on  the  land  and  breathed  air. 
When  they  perished,  their  remains  were  borne  into  the  sea  by 
torrents  and  floods;  and  they  left  for  us  the  record  of  their  exist- 
ence. With  them  we  find,  also,  the  relics  of  fishes  less  abnormal 
than  the  earlier  ones;  and  also  an  abundance  of  shells  and  corals, 
different  from  the  older  ones,  but  still  mostly  unlike  the  familiar 
forms  of  modern  times.  (Compare  Fig.  39.) 

W^e  are  rising  now  toward  the  top  of  the  series.  For  the  first 
time  we  encounter  the  remains  of  reptiles.  There  are  various  re- 
liable means  of  distinguishing  them  from  the  bones  and  teeth  of 
all  other  vetebrates.  These,  of  course,  breathed  air  and  dwelt 
mostly  on  the  land.  We  notice  a  wonderful  diversity  among 
them,  and  wre  feel  curious  to  learn  what  these  various  reptilian 
creatures  were  like.  We  shall  take  great  delight  in  studying 
them  by  and  by.  Toward  the  top  of  this  reptilian  zone,  where 
the  reptilian  remains  are  less  bulky  and  less  numerous,  we  detect 
some  relics  which  must  be  ascribed  to  birds.  In  the  midst  of 
this  zone  we  find  also  the  teeth,  bones,  and  scales  of  fishes  resem- 
bling modern  types. 

Now  we  reach  the  upper  zone  of  the  long  series  of  strata. 
Here  still  are  the  relics  of  marine  invertebrates,  of  fishes  like  the 
last,  together  with  occasional  reptiles  and  birds.  But  here  is  also 
something  very  different.  Here  are  the  bones  and  teeth  of  mam- 
malian quadrupeds.  Here  are  the  unmistakable  relics  of  land- 


FOSSILS,    A^D    WHAT   THEY   TEACH.  105 

dwellers,  which  must  have  resembled  the  modern  rhinoceros,  pig, 
sheep,  and  horse,  and  other  species  of  mammals.  It  is  easy  to 
perceive  that  they  were  not  exactly  like  our  modern  quadru- 
peds, but  they  resembled  them ;  they  were  land  animals,  and  were 
mammals. 

Notice  that  in  all  this  succession  we  have  not  found  a  bone 
or  a  tooth  which  could  be  pronounced  human.  There  is  no  rea- 
son why  human  bones  alone  should  have  disappeared.  We  are 
constrained  to  believe  that  man  did  not  exist.  All  this  succes- 
sion of  organic  forms  excluded  man.  He  has  appeared  last  of 
all,  and  all  his  remains,  and  all  the  remains  of  his  industry  lie 
upon  the  surface,  or  buried  near  the  surface,  in  deposits  laid 
down  since  the  great  work  of  rockmaking  was  ended,  except  in 
the  depths  still  submerged  beneath  the  ocean. 

Arranging  this  succession  in  a  more  synoptical  form,  and 
placing  the  older  types  at  the  bottom,  so  as  to  stand  in  the  actual 
order  of  superposition,  it  will  appear  thus: 

7.    MAN.     Remains  found  on  the  mere  surface  of  the  earth. 

6.    MAMMALS.     In  the  latest  system  of  sedimentary  rocks. 

5.  REPTILES  and  BIRDS.  In  the  middle  zone  of  the  geolog- 
ical column. 

4.    AMPHIBIANS.     The  earliest  air  breathers. 

3.    MARINE  VERTEBRATES.     Fish-like,  but  riot  true  fishes. 

2.  MARINE  INVERTEBRATES.  Molluscs,  crustaceans,  corals, 
etc. 

1.  PROTOZOANS  (in  crystalline  strata).  Simplest  of  all  ani- 
mals. 

This  succession  of  organic  types,  ranging  from  the  bottom  to 
the  top  of  the  stratigraphic  series,  is  something  very  suggestive 
and  very  important.  Let  us  think  about  it. 

1.  The  variations  among  these  fossil  remains,  from  stratum  to 
stratum,  are  much  greater  than  would  result  from  simple  changes 
in  depth  of  water  or  nature  of  the  bottom.     They  are  variations 
in  rank  and  in  class  type  and  even  in  sub-kingdom. 

2.  The  general  tenor  of  the  variations  is  an  improvement  in 
rank. 


106  GEOLOGICAL   STUDIES. 

3.  There   must  have  been,  correspondingly,  a  continuous  and 
progressive  improvement  in  the  conditions  of  the  world  in  their 
relation  to  organic  life. 

4.  The  time  demanded  for  these  changes  must  have  been  vast, 
if  we  may  judge  from  the  slowness  of  changes  taking  place  un- 
der our  observation. 

5.  In  the   earliest  ages  there  was  no  land;  all  the  species 
were  marine. 

6.  If,  as  we  have  already  inferred,  the  land  resulted  from  up- 
heaval of  sea  bottom,  it  is  probable  the  first  lands  were  of  very 
limited  extent,  and  gradually  widened  themselves  with  successive 


7.  Since  we  know  that  in  modern  times,  the  existence  of  land 
elevations  interferes  with  the  normal  circulation  of  the  waters 
and  the  atmosphere,  producing  extremes  of  seasons,  and  abrupt 
climatic    vicissitudes    throughout  the   year,  we    may   infer   that 
when  the  lands  were  less  developed,  the  seasons  were  less  extreme 
and  the  climates  more  uniform. 

8.  These  things  being  so,  the  primitive   species  of  animals 
must  have  had  a  much  wider  geographical  distribution  than  the 
later  species. 

These  conclusions,  indicated  by  our  first  glance  at  the  records 
of  historical  geology,  will  be  found  confirmed  by  all  our  later 
studies. 

The  progress  of  life  on  the  earth  supplies  the  ground  for  a 
classification  of  geological  time.  The  facts  just  stated  mark  off 
seven  grand  eras  in  the  world's  history,  as  shown  in  the  right-hand 
column  of  Fig.  39.  When  these  facts  are  combined  with  all  the 
known  facts  of  the  succession  of  life,  we  are  afforded  a  classifica- 
tion of  geological  time  as  shown  in  the  two  left-hand  columns  of 
Fig.  39.  The  larger  time  divisions  are  designated  eras  or  seons, 
and  these  are  subdivided  into  ages.  On  similar  grounds,  ages  are 
further  divided  into  periods,  as  indicated  in  the  fourth  column. 
The  rocks  receive  the  same  classification  as  time,  and  the  group- 
ings bear  the  same  special  names.  But,  for  the  general  designa- 
tions of  the  various  rock  categories,  terms  have  been  selected  ap- 


FOSSILS,    AXD    WHAT   THEY   TEACH. 


107 


GREAT  SYSTEMS, 

OR 
ERAS. 


C^NOZOIC. 


MESOZOIC. 


PALEOZOIC. 


Eozoic. 


SYSTEMS, 

OR 
AGES. 


QUATERNARY. 


TERTIARY. 


CRETACEOUS. 


JURASSIC. 


TRIASSIC. 


UPPER  CAR- 
BONIFEROUS. 


LOWER  CAR- 
BONIFEROUS. 


DEVONIAN. 


UPPER  SILU- 
RIAN 
(OR  SILURIAN). 

LOWER   SILU- 
RIAN 

(OR  CAMBRIAN). 


IIURONIAN. 


LAURENTIAN. 


GROUPS, 

OR 
PERIODS. 


Glacial. 
Pliocene. 
Miocene. 
Eocene. 

Upper  Cretaceous. 
Middle  Cretaceous. 
Lower  Cretaceous. 


Star  Peak  Group. 
Koipato  Group. 
Permian. 

Coal  Measures. 
Conglomerate 


Carbonif.  Limestone. 
CatsMll  Group. 

^g^Z~fgi2^?H      Chemung  Group. 
Hamilton  Group. 
Corniferous  Group. 
Oriskany  Sandstone. 
Helderberg  Group. 
Salina  Group. 
Niagara  Group. 

Trenton  Group. 

Canadian  Group. 
Primordial  Group. 


HIGHEST 
FOSSILS. 


FIG.  39.— THE  GEOLOGICAL  COLUMN. 


108  GEOLOGICAL   STUDIES. 

propriate  to  rock  groupings,  as  shown  at  the  heads  of  the  first, 
second  and  fourth  columns. 

The  following  scheme  illustrates  the  correlations  of  terms 
used  in  reference  to  rocks  and  time,  as  also,  the  recognized  order 
of  subordination  in  each  category: 

Time  Categories.  Rock  Categories.  Examples. 

ERAS.  GREAT  SYSTEMS.  EOZOIC,  PALEOZOIC. 

AGES.  SYSTEMS.  LAUEENTIAN,   SILURIAN. 

Periods.  Groups.  Primordial,  Canadian. 

Epochs.  Stages.  Acadian,  Potsdam,  Chazy. 

EXERCISES. 

Why  do  limestones  afford  more  fossils  than  conglomerates?  Why  do  we 
find  different  fossils  in  limestones  and  shales?  What  were  the  shales  when 
the  animal  remains  were  accumulating  in  them?  What  kind  of  sediments 
accumulate  near  the  shore?  Explain  how  changes  of  level  might  change  the 
character  of  the  sea  bottom.  How  might  the  upheaval  of  a  promontory  affect 
the  bottom  in  a  contiguous  bay?  Would  you  expect  the  remains  of  plants  to 
be  found  sometimes  embedded  in  the  strata?  Should  these  also  be  called  fos- 
sils? Would  they  be  marine  or  terrestrial  plants?  Would  terrestrial  plants 
be  more  abundant  in  the  earlier  or  the  later  ages?  Why?  Should  we  say 
"Devonian  Period"  or  "Devonian  Age"?  Correct  the  following  expres- 
sions: Primordial  System;  Hamilton  Age;  Cretaceous  Era;  Mesozoic  Pe- 
riod ;  Palaeozoic  Age ;  Chemung  Age ;  Cambrian  Group. 


STUDY   XIX.— How  the  Strata  are  Disposed. 

We  find  the  bed-rock  everywhere  —  either  at  the  surface  or 
immediately  underneath  the  unconsolidated  surface  materials. 
From  what  we  have  seen  and  reasoned  it  appears,  therefore, 
that  the  ocean  has  rested  over  every  portion  of  the  earth's 
surface.  We  have  seen  reason  to  conclude,  also,  that  there  was  a 
primitive  period  during  which  it  covered  the  whole  earth  at  once. 
The  sheet  of  sediments  then  deposited  must  have  enwrapped 
the  earth  somewhat  like  a  coat  of  an  onion  —  at  least  we  may 
assume  that  for  the  present.  But,  as  we  have  noted  evidences  of 


HOW   THE    STRATA   ABE   DISPOSED. 


109 


uplift  and  subsidence  in  the  bed  of  the  ocean,  the  primitive  sheet 
became  somewhat  irregular.  And  further,  since,  as  we  have  con- 
cluded, land  resulted  from  upheavals  of  sea  bottom,  there  must 
have  come  a  time  when  sea  sediments  were  not  deposited  over  the 
whole  earth,  for  some  portions  were  above  water.  And  finally, 
since  the  extent  of  the  land  appears  to  have  been  always  increas- 
ing, the  area  of  sea  sedimentation  has  been  continually  decreasing, 
Hence  we  understand  that  the  oldest  formations  were  universal, 
and  later  formations  have  been  successively  more  restricted  in 


FIG.  40.— ERRONEOUS  SUPPOSITION  CONCERNING  THE  STRATA. 


extent.  We  may  therefore  discover  the  limiting  borders  of  a 
formation  at  any  place  which  happened  to  be  the  sea  shore  at  the 
time  when  the  sediments  were  accumulating  out  of  which  it  has 
been  formed. 

In  addition,  it  will  be  remembered  that  erosion  of  exposed 
formations  has  always  been  in  progress.  Some  have  been  eroded 
quite  through,  as  shown  in  Fig.  38;  their  worn  edges  are  pre- 
sented to  view,  and  thus  we  discover  another  important  cause 
why  most  of  the  formations,  as  we  find  them,  are  not  of  universal 
extent. 


110 


GEOLOGICAL   STUDIES. 


We  must  not,  therefore,  conceive  the  entire  series  of  rocky 
sheets  as  enwrapping  the  earth  in  the  style  shown  in  Fig.  40. 
The  arrangements  shown  in  Fig.  41  convey  a  juster  impression; 
but  it  will  be  borne  in  mind  that  the  stratified  portion  of  the 
earth  is  vastly  less  than  here  reoresented;  and  the  disturbances, 


FIG.  41.— A  MORE  CORRECT  CONCEPTION  or  THE  STRATA  — THE  DISTURBANCES  GREATLY 
EXAGGERATED.  THE  GREAT  SYSTEMS  ARE  REPRESENTED  BY  THE  SUCCESSIVE  BANDS  : 
J.,  Eozoic;  B,  Palaeozoic;  (7,  Mesozoic;  d,  Caenozoic. 

NOTE.— The  systems  of  strata  do  not  actually  continue  under  the  deep  sea  with  un- 
diminished  thickness.    They  probably  thin  out  gradually. 

also,  greatly  less.  The  diagram  is  simply  intended  to  render 
clear  the  great  fact  of  disturbance  of  the  strata  at  successive 
epochs.  Here  it  appears  that  the  dislocations  of  the  strata 
amount  to  some  distortion  of  the  earth's  form.  The  ocean,  s  s  s, 
rests  in  the  depressions.  These  are  not  always,  at  least  under 
the  smaller  bodies  of  water,  synclinal  basins  —  that  is,  resulting 


HOW   THE    STRATA    ARE    DISPOSED.  Ill 

from  the  bending  down  of  the  strata.  Some  depressions  result 
from  erosion.  Elevations  above  the  ocean  level  constitute  the 
land.  It  also  appears  that  rocks  of  any  age  may  occupy  the  sur- 
face. The  oldest,  or  Eozoic,  may  rise  to  the  summit  of  high  ele- 
vations, or  may  lie,  or  even  outcrop,  at  much  lower  levels  than 
the  later  systems  of  strata.  This  diagram  may  be  considered  a 
section  through  the  earth.  The  exterior  portion,  showing  systems 
of  strata,  constitutes  what  is  called  the  crust.  Of  the  interior 
we  know  nothing  from  observation.  The  Eozoic  strata  which,  in 
some  places,  as  under  d  and  d" ,  lie  many  thousand  feet  deep,  in 
other  places  rise  to  the  surface,  and  thus  bring  us  information  of 
the  crust  to  such  depths  as  they  attain.  The  student  should  com- 
pare this  diagram  with  Figs.  38,  34,  33,  and  31. 

Now  we  must  explain  some  points  which  will  require  much 
patience  and  close  attention.  You  will  notice  that  the  only  sys- 
tem which  completely  surrounds  the  earth  is  the  Eozoic,  A.  The 
sediments  were  deposited  when  the  ocean  was  universal.  In  some 
places  the  Eozoic  comes  quite  to  the  surface;  in  others,  as  at 
a  a  a  a,  it  is  overlaid  by  all  the  other  systems,  because  in  those 
regions  the  Eozoic  remained  depressed  below  the  ocean  level.  In 
still  other  places,  as  at  b  b  b,  it  is  overlaid  only  by  the  Palaeozoic; 
because  either  those  places  were  not  under  the  sea  after  the  Pal- 
aeozoic aeon,  or  if  they  were,  the  later  sediments  have  been  re- 
moved by  erosion.  In  still  other  places,  as  c  c  c  c,  the  Eozoic 
is  overlaid  by  both  Palaeozoic,  .2?,  and  Mesozoic,  C;  because  those 
regions  remained  sea  bottom  during  the  Palaeozoic  and  Mesozoic 
eras,  and  no  subsequent  erosions  have  removed  the  sediments. 
There  are  only  a  few  places,  like  d  d'  d",  where  any  Caenozoic 
can  be  seen,  except  drift  or  other  Post  Tertiary,  which  covers 
nearly  all  the  land's  surface,  and  is  not  represented  in  this  dia- 
gram. The  reason  of  this  is,  that  the  sea  still  covers  nearly  all 
regions  covered  by  it  during  the  Caenozoic  aeon.  In  some  places, 
like  d' ,  the  Tertiary  (Caenozoic)  rests  directly  upon  the  Palaeo- 
zoic, or  even  the  Eozoic.  This  is  because  after  the  older  strata 
were  deposited,  the  region  became  dry  land,  and  received  no  more 
sediments  till  the  Caenozoic  aeon,  when  the  region  subsided  and 


112  GEOLOGICAL   STUDIES. 

again  became  sea  bottom.  Thus  a  break  in  the  succession  of 
formations  generally  implies  a  period  of  elevation,  followed  by  a 
period  of  subsidence. 

If  you  look  closely  at  this  diagram,  you  will  notice  an  ap- 
pearance as  if  the  Palaeozoic  and  Mesozoic  strata  had  at  some 
former  time  extended  further  than  at  present.  For  instance,  the 
dotted  line,  c'  cf,  shows  what  may  have  been  at  some  time  the 
upper  surface  of  the  Mesozoic.  If  so,  then  the  dotted  line  below 
this  shows  what  may  have  been  at  the  same  time  the  upper  sur- 
face of  the  Palaeozoic.  In  fact,  on  all  sides  the  arrangement  of 
the  strata  looks  as  if  they  had  been  once  wrinkled  up,  and  then 
the  higher  places  removed.  This  is  somewhat  like  the  truth;  but 
we  must  not  suppose  the  Palaeozoic  and  Mesozoic  ever  extended 
quite  over  all  the  Eozoic  which  is  now  at  the  surface.  We  can- 
not say  precisely  how  far  they  ever  covered  the  Eozoic,  because 
it  is  impossible  to  say  how  far  they  have  been  removed  by  erosion. 
We  are  certain,  however,  that  they  have  been  eroded  to  a  great 
extent.  And  we  can  understand  that  the  sediment  produced  by 
such  erosions  went  partly  into  the  sea,  and  was  made  over  in  the 
patches  of  tertiary  which  we  observe  at  d  d  d'  d". 

If  the  dotted  circle,  s  s  s,  represents  the  level  of  the  ocean, 
you  can  see  that  some  parts  of  the  crust  rise  above  it  and  form 
the  continents;  and  those  parts  which  rise  highest  are  the  moun- 
tains. You  see,  also,  that  all  the  systems  of  strata  extend  under 
the  sea. 

Now  fix  your  attention  on  the  d  near  the  lower  side  of  the 
diagram,  a  little  to  the  left  of  the  middle.  The  rocks  there  are 
Caenozoic,  and  you  see  a  section,  or  cut,  right  through  them  and 
the  rocks  under  them.  This  section  shows  what  is  the  surface 
extent  of  the  Caenozoic  area  there,  in  one  direction.  Here  it  is 
—  the  distance  from  m  to  n  in  this  little  cut,  Fig.  42.  We  do 
not  know  how  broad  this  Caenozoic  area  is  in  the  other  direction, 
but  let  us  suppose  it  a  little  oblong  in  form;  then  its  other  diam- 
eter may  be  represented  by  o  p;  and  m  p  n  o  will  be  a  map  of 
the  Caenozoic  area  of  which  a  section  is  shown  in  Fig.  41  at  <7, 
near  the  lower  side  of  the  figure.  But  then  on  one  side,  #, 


HOW   THE   STRATA    ARE    DISPOSED. 


113 


FIG.  42.— MAP  OF  THE  REGION 
AROUND  b  dc,  FIG.  41. 


of  this  Csenozoic  section  is  a  section  of  Mesozoic  strata.  Let  us 
take  the  length  of  this  Mesozoic  section  and  lay  it. off  from  m  to 
r  on  the  side  of  the  map,  Fig.  42. 
As  the  Mesozoic  on  the  other  side  is 
covered  by  the  sea,  we  may  represent 
the  sea  as  bordering  the  C£enozoic? 
and  may  lay  down  as  much  of  it  as 
we  please  —  say  from  n  to  q,  on  the 
other  side  of  the  map;  and  may  as- 
sume that  the  sea  shore  leaves  the 
Csenozoic  area  at  s  s.  Then  the  dis- 
tance from  r  across  to  n  is  the  whole 
diameter  of  the  Mesozoic  area  to  the 
sea,  including  the  portion  covered  by 
the  Csenozoic.  The  breadth  in  the 
other  direction  is  not  known;  but 
we  may  assume  it  as  extending  from 
t  to  u.  The  whole  size  of  the  Meso- 
zoic area  not  covered  by  the  sea  will  be  shown  by  v  t  r  u  w. 
Lastly,  the  Paleozoic  when  laid  down  on  a  map  will  give  a  belt 
surrounding  the  Mesozoic,  as  shown  on  x  y  z.  So  this  is  a  geo- 
logical map  showing  three  systems  of 
strata;  and  Fig.  43  shows  the  appearance 
of  a  section  across  it. 

Now,  once  more.  Fix  your  attention 
on  the  point  6r  in  Fig.  41.  If  we  pro- 
ceed to  make  a  map  of  the  region  around 
this  point,  it  will  look  something  like  Fig.  44.  Here  you  see  the 
Eozoic  in  the  middle,  and  the  newest  strata  around  the  border. 
Here,  also,  the  ocean  bounds  the  area  on  one  side.  Notice  par- 
ticularly the  difference  between  this  map  and  the  other.  There 
the  strata  dipped  from  all  sides  toward  the  centre;  here  they  dip 
from  the  centre  toward  all  the  sides.  This  is  shown  in  the  sec- 
tion as  seen  at  6r,  Fig.  41,  and  better  in  Fig.  45.  Here  the 
Mesozoic,  c,  dips  under  the  ocean,  s,  on  one  side,  and  under 
the  Csenozoic,  d,  on  the  other;  the  Palaeozoic,  b,  dips  under  the 


FIGS  43.— SECTION  ALONG  THE 
LINE  y  q,  FIG.  42. 


114 


GEOLOGICAL   STUDIES. 


Caenozoic,  c,  extending  on  one  side  under  the  ocean;  the  Eozoic, 
G,  dips  in  both  directions  under  the  Palaeozoic.  From  such  ob- 
servations we  induce  the  impor- 
tant principle  that  the  dip  of 
a  formation  is  always  toward 
newer  rocks  and  away  from 
older  rocks. 

Now,    for    a    more    detailed 
and    extensive    section    through 
the  earth's  crust,  let  us  glance 
at  Fig.  46.     This  is  not  intended 
to  show  what  would  be   seen  in 
any  particular  region,  but  what 
would   be   seen   in  a  good  many 
different    regions.     The    various 
geological      phenomena      which 
would   be   seen   in  many   differ- 
ent regions  are  here  all  brought 
together.      So  this  is  not  a  real 
But  the  section  is  not  imaginary.     Every- 
It  embraces  many  features  to 
be    considered     later     in     our 

-° — ~ —  be          .<?          course,  and  we  shall  frequently 

refer  to  it.  For  the  present, 
it  illustrates  in  another  way 
the  succession  of  strata,  and 
their  modes  of  superposition 
and  outcrop. 


FIG.  44. — MAP  or  THE  REGION  AROUND 
G,  FIG.  41. 

but  an  ideal  section. 

thing  shown  is  real   somewhere. 


FIG.  45. — SECTION  ALONG  THE  LINE  d  s, 
FIG.  44. 


EXERCISES. 

In  Fig.  42,  if  we  travel  from  the  centre  to  the  circumference,  do  we  pass 
from  newer  to  older  rocks,  or  from  older  to  newer?  If  we  stand  near  the 
circumference,  which  way  do  the  strata  dip?  Do  they  dip  to  ward  and  under 
newer  strata,  or  away  from  them  ?  If  we  bore  a  deep  hole  at  the  centre  of 
Fig.  42,  what  systems  of  rocks  will  we  pass  through?  If  we  stand  near  the 
circumference  of  Fig.  44,  which  way  do  the  rocks  dip?  Do  they  dip  toward 


I 

FIG.  46.— IDEAL  SECTION  OF  THE  EARTH'S  CRUST. 


116  GEOLOGICAL  STUDIES. 

the  older  rocks,  or  away  from  them?  Must  strata  always  dip  toward  newer 
rocks,  and  away  from  older  rocks?  Suppose  you  bore  a  deep  hole  near  the 
margin  of  Fig.  44,  what  systems  of  strata  would  be  passed  through  ?  Sup- 
pose you  bore  at  the  middle  of  Fig.  44,  what  rocks  will  be  passed  through? 
Must  a  geological  area  necessarily  be  circular?  Suppose  the  ocean  should 
wear  away  two-thirds  from  the  area  mapped  in  Fig.  44,  could  you  then  make 
a  geological  map  of  the  region?  Try  it.  Point  out  places  where  the  Palaeo- 
zoic outcrops  in  Fig.  41.  Show  where  the  Eozoic  outcrops.  What  system  of 
rocks  least  completely  enwraps  the  earth?  How  could  it  be  that  Caenozoic 
rocks  should  rest  on  Eozoic,  with  no  Palaeozoic  or  Mesozoic  between  them? 
Make  a  geological  map  of  the  region  extending  from  G  toward  the  left, 
through  c,  d,  and  s  to  b,  in  Fig.  41. 


STUDY  XX.—  Geological  Maps. 

The  subject  of  geological  maps  is  another  one  requiring 
thoughtful  attention,  but  one  of  the  very  greatest  importance. 
The  comprehension  of  geological  maps  is  a  great  aid  in  the  com- 
prehension of  geological  facts  and  doctrines.  In  our  last  Study 
you  observed  small  areas,  as  in  Figs.  42  and  44,  marked  in  such  a 
wav  as  to  indicate  the  regions  where  certain  systems  of  strata 
come  to  the  surface.  You  understand,  from  Figs.  ,38  and  41,  that 
no  formation  occupies  the  surface  universally —  for  we  except  the 
quaternary,  or  drift.  You  understand  that  each  formation  comes 
to  the  surface  in  many  different  places,  and  in  other  places  is  cov- 
ered by  newer  formations,  or  was  never  deposited.  You  under- 
stand, consequently,  that  the  whole  surface  of  the  land  is  com- 
posed of  areas  of  outcrop  of  the  various  formations.  We  may, 
therefore,  take  a  map,  and  color  or  mark  these  various  areas  ac- 
cording to  the  formations  which  come  to  the  surface.  Now,  most 
that  we  can  learri  about  the  earth's  geology  comes  from  a  study 
of  surface  formations.  If  we  are  seeking  for  coal,  or  iron,  or  fos- 
sils, we  can  do  but  little  more  than  study  the  formations  at  the  sur- 
face. Hence,  a  geological  map  of  the  surface  conveys  most  im- 
portant information.  The  geological  investigation  of  a  region 
consists  very  largely  in  perfecting  a  geological  map  of  it. 


GEOLOGICAL   MAPS.  117 

Now,  I  wish  to  offer  you  a  geological  map  of  the  United  States. 
The  map,  Fig.  47,  covering  two  pages,  embraces  the  whole  United 
States  except  Alaska,  though  it  must  be  confessed  some  of  the 
region  west  of  the  Black  Hills  is  delineated  only  in  a  very  gen- 
eral way.  This  is  a  real  map,  which  attempts  to  represent  things 
as  they  are  —  though  not  with  much  detail.  In  one  corner  is  a 
"legend,"  which  indicates  what  systems  of  strata  are  mapped. 
These  are  the  same  as  the  "  systems  "  in  the  "  Geological  Col- 
umn," Fig.  39,  with  these  exceptions:  The  Laurentian  and  Hu- 
ronian  are  here  thrown  together  as  Eozoic;  theTriassic  and  Juras- 
sic are  thrown  together  as  Jura-trias,  and  the  Post  Tertiary  (or 
Quaternary)  is  disregarded,  except  in  some  districts  west  and 
southwest  of  Great  Salt  Lake,  since  this  is  understood  to  be  every- 
where present,  covering  all  other  formations. 

Taking  up  the  eastern  portion  of  this  map,  fix  your  attention 
first  on  the  areas  marked  Eozoic.  One  large  area  lies  north  of  the 
Great  Lakes  and  the  St.  Lawrence  River  ;  another  lies  along  the 
eastern  flanks  of  the  Appalachian  chain  of  mountains,  extending 
from  Pennsylvania  through  Maryland,  Virginia,  North  and  South 
Carolina  and  Georgia,  into  Alabama.  These  two  Eozoic  masses 
pass  under  all  the  intervening  strata,  and  meet  together.  As  the 
Eozoic  strata  are  the  oldest  known,  the  strata  on  both  sides  of  an 
Eozoic  area  must  be  newer  than  Eozoic,  and  must  overlie  the 
Eozoic.  As  the  dips  are  always  away  from  the  older  rocks,  it 
must  be  that  the  rocks  along  the  eastern  side  of  the  Appalachian 
Eozoic  dip  toward  the  southeast,  and  those  along  the  western 
side  toward  the  northwest.  And  so  the  rocks  along  the  border 
of  the  Canadian  Eozoic  must  dip  directly  away  from  it.  That  is, 
along  the  valley  of  the  St.  Lawrence  River,  the  rocks  next  the 
Eozoic  must  dip  southeast  ;  in  the  region  north  of  Lakes  Ontario 
and  Huron,  the  dip  must  be  south  ;  in  eastern  Wisconsin,  the  dip 
is  southeast,  and  in  western  Wisconsin  it  is  southwest. 

Southeast  from  the  Appalachian  Eozoic,  we  have  very  little 
except  Tertiary  strata.  These,  then,  overlie  the  border  of  the 
Eozoic,  and  dip  southeastward,  extending  to  the  Atlantic  Ocean. 
Northwest  of  the  Appalachian  Eozoic,  we  find  strata  indicated  by 


GEOLOGICAL   MAPS. 


119 


FIG.  47.— CONTINUED. 


120  GEOLOGICAL   STUDIES. 

full  oblique  lines  in  one  direction,  and  broken  oblique  lines  in  the 
other  direction.  These  are  explained  in  the  "  legend  "  to  mean 
that  the  rocks  are  either  Cambrian  or  Silurian  (Lower  Silurian  or 
Upper  Silurian,  as  some  geologists  prefer  to  say),  but  we  have  not 
yet  ascertained  which.  These  must  dip  northwesterly,  away  from 
the  older  Eozoic,  and  toward  the  newer  Upper  Carboniferous. 
Passing  under  all  the  Carboniferous,  they  come  to  the  surface 
again  in  Tennessee,  Kentucky,  Ohio  and  Indiana,  where  we  have 
learned  them  well  enough  to  distinguish  both  Cambrian  and  Silu- 
rian (or,  as  some  say,  Lower  and  Upper  Silurian).  On  the  north, 
Cambrian  and  Silurian  come  up  along  the  two  shores  of  Lake 
Ontario.  From  this  region  the  dip  is  southward  all  the  time  un- 
til we  reach  central  Pennsylvania.  In  southwestern  Ohio,  the 
Cambrian,  which  comes  up  from  the  southeast,  soon  dips  down 
again  toward  the  northwest,  and  passing  under  Michigan  and 
Lake  Michigan,  comes  up  again  in  eastern  Wisconsin.  Now,  try 
and  follow  the  Cambrian  and  Silurian  up  and  down  all  the  way 
from  the  Appalachian  Eozoic. 

You  must  not  be  content  to  simply  read  these  descriptions. 
You  must,  by  all  means,  follow  the  systems  of  strata  on  the  map. 
When  they  go  under,  your  thoughts  must  follow  them.  When 
they  appear  in  view  again,  your  thoughts  must  see  them  coming 
from  under  the  newer  strata.  You  must  look  under  the  surface 
of  the  map  and  see  the  solid,  thick  crust  of  the  earth,  with  its 
various  strata  curved  and  overlapping,  and  discontinuing  and  be- 
ginning again,  disappearing  and  outcropping,  just  as  I  describe 
them.  If  you  do  this,  and  perform  an  abundance  of  such  exer- 
cises as  will  be  given  you,  the  study  will  soon  be  easy  and  delight- 
ful. If  you  do  not,  you  will  never  have  a  good  knowledge  of 
geology. 

Now  let  us  continue  the  explanation  of  the  map.  On  the 
southwestern  border  of  the  Wisconsin  Eozoic  you  see  Cambrian 
overlying  it,  arid  thence  dipping  southwesterly  under  Silurian, 
Devonian,  Lower  Carboniferous,  and  Upper  Carboniferous.  We 
can  trace  it,  in  thought,  under  all  these  systems,  into  Missouri  and 
Kansas.  We  might  reasonably  expect  the  Eozoic  to  come  to  the 


GEOLOGICAL   MAPS.  121 

surface  again  in  the  region  farther  southwest,  but  it  scarcely  suc- 
ceeds in  revealing  itself.  You  will  notice  one  patch  in  the  Ind- 
ian Territory,  and  one  in  southern  Texas  ;  but  nearly  all  that 
region  has  been  covered  by  Jura-trias,  and  then  most  of  that  has 
been  covered  by  Cretaceous.  Even  upon  the  top  of  the  Creta- 
ceous are  some  patches  of  Tertiary. 

In  New  England  you  will  notice  considerable  areas  marked 
Eozoic;  but  in  some  cases  we  only  know  that  the  rocks  are  crys- 
talline like  Eozoic,  while  they  may  be  in  reality  only  later  rocks 
hardened  and  crystallized  by  metamorphism.  You  observe,  how- 
ever, a  patch  of  Upper  Carboniferous  in  Rhode  Island,  and  a  belt 
of  Jura-trias  running  through  Connecticut  and  Massachusetts. 
Farther  north  you  will  notice  that  the  valley  of  the  Connecticut 
is  underlaid  by  Cambro-silurian  rocks  —  that  is,  rocks  either  Cam- 
brian or  Silurian. 

In  the  Adirondack  region  of  New  York  is  an  interesting 
Eozoic  area.  This  connects  with  the  Canadian  Eozoic  by  a  nar- 
row neck  across  the  St.  Lawrence  River.  The  strata  all  around 
this  Adirondack  area  dip  away  from  it.  This  is  a  case  somewhat 
like  the  Eozoic  area  in  Wisconsin.  On  the  other  hand,  the  centre 
of  Michigan  is  an  area  of  Upper  Carboniferous,  and  since  the 
surrounding  strata  are  all  older  they  all  dip  toward  the  centre  of 
Michigan. 

Now  let  us  vary  the  method  of  study.  Suppose  we  stand  on 
the  southern  side  of  Lake  Ontario,  the  map  shows  that  the  dip 
of  the  rocks  is  south;  for  at  that  point  we  have  Silurian,  while  to 
the  south  are  the  (newer)  Devonian  and  Lower  and  Upper  Car- 
boniferous; and,  according  to  the  rule,  the  dip  is  toward  the 
newer  and  away  from  the  older  in  Canada. 

If  we  stand  at  Milwaukee,  the  dip  is  eastward,  for  Milwaukee 
is  on  the  Silurian,  and  eastward  we  have  the  Devonian  and  Lower 
and  Upper  Carboniferous  in  Michigan.  Lake  Michigan  must  also 
cover  a  portion  of  the  Silurian  and  much  of  the  Devonian.  If, 
on  the  contrary,  we  stand  at  the  St.  Clair  River,  the  dip  is  west- 
ward on  the  same  principle. 

Again,  if  we  stand  at  Sandusky,  Ohio,  we  are  on  the  Silurian; 


122  GEOLOGICAL   STUDIES. 

and  if  we  walk  straight  to  Cincinnati,  we  walk  a  long  distance  on 
Silurian,  and  then  come  to  Cambrian.  Then,  if  we  continue  our 
travel  to  Nashville,  Tenn.,  we  pass  again  over  Silurian,  a  narrow 
belt  of  Devonian,  a  broad  belt  of  Lower  Carboniferous,  and  then 
come  to  a  very  narrow  streak  of  Silurian  again  (too  narrow  to 
show  on  the  map  at  this  place,  though  it  can  be  seen  south  of 
the  Cumberland  River),  and  end  our  journey  on  the  Cambrian. 
Should  we  continne  southward  to  Mobile,  we  should  pass  off  the 
Cambrian  directly  upon  the  Lower  Carboniferous,  which  extends 
into  Alabama.  Then,  in  the  neighborhood  of  Tuscaloosa,  we 
should  pass  upon  the  Upper  Carboniferous,  and  beyond  this,  to 
the  overlying  Cretaceous,  and  should  find  Mobile  on  the  Tertiary. 
If  we  should  travel  from  Albany  to  Boston,  we  should  start 
on  Cambrian  rocks  and  pass  to  Silurian  rocks.  Before  reaching 
central  Massachusetts  we  should  pass  to  rocks  which  are  not  fully 
determined  —  perhaps  Cambro-silurian  —  and  perhaps  an  outcrop 
of  Eozoic.  Crossing  the  valley  of  the  Connecticut  would  be  found 
Jura-trias  rocks  resting  horizontally  in  a  trough  excavated  in  the 
older  rocks.  Those  on  the  map  are  not  extended  far  enough 
north.  Beyond  this  valley  we  should  find  again  rocks  which  are 
perhaps  Cambro-silurian.  Beyond  these  we  should  have  Eozoic 
rocks  for  the  greater  part  (all  Eozoic  on  the  map)  until  reaching 
Boston.  All  these  things,  and  a  thousand  others,  may  be  studied 
out  on  the  map. 

EXERCISES. 

If  you  travel  in  a  straight  line  from  Detroit  to  Milwaukee,  what  systems 
of  strata  will  you  pass  over?  What  if  you  travel  from  Mackinac  to  Cincin- 
nati? What  between  Oswego  and  Plattsburg?  What  between  Charleston 
and  Nashville?  State  the  dip  of  every  system  of  strata  passed  between  St. 
Louis  and  Chicago.  Between  Duluth  and  Lake  Michigan.  Between  Sagi- 
naw  and  Springfield,  111.  Between  Springfield  and  Cincinnati.  Between 
Cleveland  and  Pittsburgh.  What  is  the  dip  of  the  strata  at  Cleveland? 
What  at  Green  Bay?  What  at  Binghamton,  N.  Y.  ?  What  at  Utica,  N.  Y.  ? 
Suppose  you  bore  an  artesian  well  at  Lansing,  Mich.,  what  systems  of  strata 
will  be  passed  through  ?  What  if  you  bore  at  Charleston,  S.  C.  ?  What  if  you 
bore  at  Hartford,  Conn.  ?  What  if  you  bore  at  Peoria,  111.  ?  What  if  you 
bore  at  Galveston,  Texas?  What  if  you  bore  at  Montreal,  Canada?  Would 


GEOLOGICAL   SECTIONS.  123 

an  artesian  well  bored  at  Cincinnati  pass  through  the  Silurian  ?  Or  the  De- 
vonian? How  could  you  travel  from  Albany,  N.  Y.,  to  St.  Paul  without 
passing  off  the  Cambro-silurian  ?  How  from  Cairo  to  Cape  May  without 
passing  off  the  Tertiary?  How  many  great  patches  of  Upper  Carboniferous 
(Coal  Measures)  are  shown  on  the  map?  Into  what  states  does  the  Appalach- 
ian coal  area  reach?  Into  what  states  the  Illinois  coal  area?  Into  what  the 
Kansas  coal  area?  Into  what  the  Michigan?  Into  what  the  Rhode  Island? 
Which  state  has  the  largest  area  of  Eozoic  rocks?  Which  next?  Which  has 
the  largest  area  of  Tertiary  ?  Which  state  contains  the  greatest  number  of 
different  systems?  Which  contains  the  fewest  different  systems?  What 
states  have  the  largest  amount  of  soft  rocks?  What  ones  have  most  Paleo- 
zoic rocks?  Give  the  names  of  the  cities  indicated  by  black  dots  on  the  map, 
and  state  what  system  of  rocks  each  is  located  on. 

NOTE.— The  student,  during  his  elementary  course,  ought  to  construct  a  geological 
map  of  the  eastern  United  States,  covering  about  the  same  ground  as  the  one  here  pre- 
sented. It  would  be  desirable  to  make  it  on  a  larger  scale,  and  also  to  employ  a  system 
of  colors  as  indicated  in  the  introduction. 


STUDY  XXL—  Geological  Sections. 

The  student  cannot  take  too  many  exercises  on  the  geological 
map.  He  should  become  familiar  as  possible  with  the  surface 
distribution  of  the  formations.  This  is  geographical  geology. 
Such  a  map  is  a  picture  of  the  geology  at  the  surface.  But,  at 
the  same  time,  a  careful  study  of  it  leads  to  important  inferences 
in  reference  to  the  deeper  geology.  So  you  must  not  be  con- 
tent to  look  merely  upon  the  flat  surface  of  the  map.  It  is  not 
enough  even  to  learn  the  location  of  the  different  colors  lying  on 
the  surface.  You  must  think  of  each  color  or  system  of  mark- 
ings as  an  outcropping  of  something  which  goes  down  beneath 
the  surface  to  some  other  region,  where  it  outcrops  again.  You 
must  think  which  way  it  goes  beneath  the  surface  —  that  is,  what 
is  its  dip.  The  rule  already  given  determines  that.  So  when 
you  look  on  the  geological  map,  you  will  learn  to  look  into  it, 
and  far  beneath  the  surface.  You  will  see  the  whole  solid  frame- 
work of  the  rocks  which  underlie  a  country. 

Now,  we  shall  undertake  some  exercises  which  will  give  us 
the  power  of  penetrating  into  the  depths  of  the  solid  crust. 


124  GEOLOGICAL   STUDIES. 

With  the  geological  map  before  us,  we  will  try  to  construct 
some  geological  sections.  That  is,  if  we  could  cut  straight  down 
along  the  line  between  two  points  which  may  be  selected,  to  the 
depth  of  some  thousands  of  feet,  and  then  look  at  the  cut  edges 
of  the  strata,  what  form  and  arrangement  would  they  present 
to  us  ? 

To  begin  with  a  simple  case,  let  us  construct  a  section  across 
the  state  of  Michigan  from  Detroit  to  Grand  Haven.  We  will 
first  draw  a  line,  G  D,  Fig.  48,  to  represent  the  distance  along 
the  surface  between  the  two  points.  We  suppose  ourselves 
facing  north.  We  notice  that  Detroit  stands  on  the  Devonian. 

G  c  b  a  D  Take  the  distance  from  Detroit  to  the  west- 
FIG.  ^'.'-PREPARING  FOR  QTn  border  of  the  Devonian,  and  lay  it  off 
A  GEOLOGICAL  SEC-  from  D  on  the  line  G  D.  This  distance 
extends  to  a.  Next,  lay  off  from  a  the  dis- 
tance which  corresponds  to  the  breadth  of  the  Lower  Carbonifer- 
ous in  the  direction  from  Detroit  to  Grand  Haven.  This 
stretches  to  b.  Thirdly,  lay  off  the  distance  which  our  route 
passes  over  the  Upper  Carboniferous.  This  takes  us  to  c.  Fourth- 
ly, lay  off  the  distance  to  the  western  border  of  the  Lower  Car- 
boniferous; this  takes  us  to  d.  Finally,  lay  off  the  short  distance 
to  Grand  Haven,  on  the  border  of  Lake  Michigan.  This  takes 
us  to  G. 

Next,  we  have  to  consider  what  is  the  dip  of  the  strata  at 
each  point.  On  our  principles,  the  dip  is  toward  the  Upper  Car- 
boniferous from  both  ends  of  the  line.  Draw  lines  down  oblique- 
ly, according  to  the  dip,  from  a,  b,  c,  and  d,  Fig.  49,  the 
boundary  points  between  the  formations. 
\^^\^.=^^1 — \  Then,  knowing  that  the  Lower  Carboniferous, 

^ """i       which   dips    down  westward    in    the    eastern 

FIG.    49. —  PROGRESSING  „    .  ,  ,  .   . 

WITH   A   GEOLOGICAL    Part  of  the  state,  is  the  same  which  comes  up 

SECTION.  to    the    surface    from    the    eastward,    in    the 

western  part  of  the  state,  we  can  connect  the  lines  representing 
the  lower  and  upper  surfaces  of  this  system.  That  is,  the  upper 
line  will  extend  from  b  to  c,  passing  down  under  the  Upper  Car- 
boniferous; and  the  lower  line  will  extend  from  a  to  d,  passing 


GEOLOGICAL   SECTIONS.  125 

under  both  Upper  and  Lower  Carboniferous.  The  dip  of  the 
strata  from  D  must  pass  in  the  same  direction  as  from  a  and  b. 
But  notice  that  Detroit  is  not  on  the  eastern  limit  of  the  Devo- 
nian. The  line  from  the  eastern  limit  —  wherever  it  is  —  will 
pass  some  distance  under  Detroit,  as  at  e.  We  need  not  know 
where  it  comes  up  to  the  surface.  It  is  somewhere  to  the  east- 
ward, but  we  may  cut  it  off  at  e,  as  we  are  only  required  to  con- 
struct the  section  to  Detroit.  That  line,  then,  ending  at  e,  shows 
the  bottom  of  the  Devonian.  Passing  westward,  it  will  come  up 
at  the  west  side  of  the  Devonian,  wherever  that  is.  But  the  first 
system  west  of  Lake  Michigan  is  the  Silurian,  and  the  place  for 
the  bottom  of  the  Devonian  is  between  it  and  d,  near  Grand 
Haven.  The  western  outcrop  of  the  bottom  of  the  Devonian 
seems  to  be  in  the  bottom  of  Lake  Michigan.  This  belief  is  con- 
firmed by  observing  that  on  the  map,  the  outcrop  of  the  Devonian 
strikes  the  south  end  of  Lake  Michigan,  and  seems  to  pass  under 
the  lake.  It  comes  mostly  from  under  the  lake  again  in  the 
region  of  Grand  Traverse  and  Little  Traverse  Bays,  and  Macki- 
nac.  We  will  therefore  assume  that  the  western  outcrop  of  the 
Devonian  is  under  the  lake.  We  will  also  draw  a  little  depres- 
sion to  represent  the  bed  of  the  lake. 

Instead  of  seeking  for  the  western  outcrop  of  the  bottom  of 
the  Devonian,  we  might  say  as  we  did  about  the  eastern  outcrop, 
that  it  does  not  concern  us  to  find  it;  we  know  the  bottom  line 
passes  at  some  distance  under  6r,  and  in  that  position  we  may 
draw  it,  and  let  fall  a  perpendicular  from  G  to  it  —  as  from  D 
to  e. 

So  far  we  have  assumed  that  the  surface  of  the  earth  is  a  dead 
level  from  Detroit  to  Grand  Haven;  but,  if  we  happen  to  know 
that  the  center  of  the  state  swells  up  a  little,  we  should  so  repre- 
sent it.  We  ought,  indeed,  to  know  this;  because,  if  you  look  on 
any  map  of  Michigan,  you  see  the  streams  all  flowing  from  the 
interior  into  the  surrounding  lakes.  If,  then,  we  show  the  sur- 
face configuration,  our  section  will  be  a  geological  profile. 
Here  it  is  in  Figure  50,  but  on  a  scale  twice  as  large.  In 
completing  the  section  we  may  bear  in  mind  that  the  Silurian, 


126 


GEOLOGICAL   STUDIES. 


which  outcrops  at  Milwaukee,  passes  under  Lake  Michigan  and 
the  state  of  Michigan,  and  we  may  so  represent  it,  though  a  sec- 
tion across  Michi- 
gan  does  not  re- 
quire this.  It  would 
be  proper,  also,  to 
represent  the  Cam- 

FIG.  50.— COMPLETED  GEOLOGICAL  SECTION  BETWEEN  DE-     brian  under  the  Silu- 
TKOIT  AND  GRAND  HAVEN,  MICH. 

nan,    since    we    see 

from  the  map  that  on  the  west  of  Milwaukee  it  passes  eastward 
under  the  Silurian.  And,  finally,  we  notice  that  in  central  Wis- 
consin the  Eozoic  passes  southward  under  the  Cambrian;  and  we 
may  fairly  assume  that  it  would  appear  beneath  the  Cambrian 
under  Michigan  if  we  were  able  to  make  actual  examination. 
So  we  fill  in  the  lower  left-hand  corner  of  our  section  with  the 
marks  indicating  Eozoic.  Now  the  section  is  complete. 

We  have,  in  fact,  extended  the  section  farther  west  than  was 
required.  We  might  have  cut  it  off  at  Grand  Haven.  Also,  we 
have  carried  it  deeper  than  necessary.  All  that  is  essential  in  a 
section  from  Detroit  to  Grand  Haven  is  shown  by  the  broken 
lines. 

Next,  let  us  construct  a  geological  section  from  the  Eozoic 
north  of  Lake  Ontario  to  Williamsport,  on  the  Coal  Measures  of 
Pennsylvania;  and  let  us  suppose  ourselves  facing  east.  Draw  a 
line,  E  Wy  Fig.  51,  to  represent  the  length 
of  the  section.  This  may  be  the  same  length 
as  the  distance  on  the  map,  or  any  multiple 
of  that  distance.  However  the  length  of  the 
line  chosen  compares  with  the  distance,  all 
the  intervening  distances  must  be  in  the  same  proportion;  or,  if 
we  know  the  distances  in  miles,  we  may  lay  them  off  from  a 
scale.  The  number  of  miles  may  be  got  from  a  "  scale  of  miles  " 
given  on  a  good  map.  When  this  is  done,  allow  a  little  space  — 
the  proper  space,  if  known  —  to  the  right  of  E  for  the  distance 
to  the  southern  margin  of  the  Eozoic;  and  fix  on  a  point,  a,  for 
the  border  of  the  Cambrian.  The  dividing  line  between  the  Cam- 


E 


FIG.  51. — PREPARING 
FOR  A  GEOLOGICAL 
SECTION. 


GEOLOGICAL   SECTIONS.  127 

brian  and  Silurian  is  under  the  lake;  let  us  locate  it  under  b. 
The  southern  limit  of  the  Silurian  will  be  at  c.  The  southern 
limit  of  the  Devonian,  determined  from  the  map,  will  be  at  d  • 
and  here  the  Lower  Carboniferous  begins.  The  southern  limit  of 
the  Lower  Carboniferous,  which  is  the  northern  limit  of  the  Upper 
Carboniferous,  will  be  at  e.  Then  the  southern  extremity  of  our 
section  will  be  at  TFi  just  over  the  border  of  the  Coal  Measures. 

Now,  we  understand  that  all  these  rocks  dip  southward.     So 
we   draw  lines    from    the   points   a  b  c  d  e, 
Fig.  52,  to  represent  the  dip,  and  terminate 
downward  at  such  points  as  to  produce  a  neat 
figure  showing    all  that  is  required.       Then     FIG.  52.—  PROGRESSING 

we  may  fill  in  the  lines  and  characters  chosen        WITH  A  GEOLOGICAL 

,  .  SECTION. 

to  represent  the  various  systems. 

Notice,  that  it  is  customary  to  represent  the  dip  somewhat 
greater  than  the  reality,  unles  the  real  dip  is  steep  enough  to  give 
a  convenient  breadth  to  the  section.  Notice,  also,  that  this  makes 
the  thicknesses  of  the  formations  too  great  to  be  in  due  propor- 
tions to  the  distances  along  the  surface.  The  section  therefore 
has  a  "  vertical  scale  "  greater  than  the  "  horizontal  scale,"  and 
the  section  is  a  distorted  one,  not  a  natural  one.  We  always 
make  the  two  scales  the  same  if  practicable. 

We  have  constructed  this  section  thus  far  on  the  assumption  of 
a  dead  level  from  end  to  end.  But  we  ought  always  to  represent 
the  relative  elevations  of  different  points  as  well  as  we  can.  In 
fact,  geologists  often  take  very  great  pains  to  ascertain  the  levels 
of  different  points.  If  the  region  where  E  is  located  is  some- 
what elevated,  we  should  so  represent  it.  And  if  we  know  that 
a  high  bluff  of  strata  extends  along  the  south  shore  of  Lake  On- 
tario, we  should  so  represent  that.  An  improved  section  between 
the  two  points  would  be  as  shown,  Fig.  53.  This  is  made  on  a 
scale  four  times  as  large  as  the  other,  which  is  too  small  for  con- 
venience. Here  we  notice  a  surface  slope  from  north  and  from 
south  toward  Lake  Ontario.  Also  a  slope  from  both  directions 
toward  the  Chemung  River,  whose  place  is  shown  by  e.  These 
things  are  not  all  shown  on  the  geological  map;  but  if  you  can, 


128 


GEOLOGICAL   STUDIES. 


in  any  way,  obtain  information  about  the  configuration  of  the 
surface,  that  should  be  introduced  into  your  section.  You  will 
often  have  to  refer  to  your  geographical  atlas  to  learn  where 
places  mentioned  are  located.  The  directions  in  which  streams 
run  will  also  show  you  what  regions  are  more  elevated  and  what 
are  less  elevated.  The  surface,  also,  always  slopes  toward  streams. 
The  region  between  streams  is  always  somewhat  elevated;  but 
the  amount  of  elevation  is  less  in  a  country  nearly  level  than  in 
one  having  considerable  slope. 

The  following  is  the  way  we  complete  the  geological  pro- 
file. Having  laid  down  the  necessary  points  along  a  horizontal 
line  A  JB,  draw  vertical  lines  from  these  points,  as  shown,  Fig.  53, 
and  draw  as  exactly  as  you  can,  a  line  E  P  to  represent  the 
surface  of  the  earth.  The  points  a  c  d  ey  where  this  line  inter- 


FIG.  53.— COMPLETED  GEOLOGICAL  SECTION. 
E,  Canadian  Eozoic ;  Co,  Coburg;  R,  Rochester;  tf,  Corning;  W,  Williamsport. 

sects  the  vertical  lines,  indicate  the  bounds  of  the  different  form- 
ations. From  these  points  we  may  draw  lines  to  represent  the 
dip  and  the  thickness  of  each  formation.  (Those  who  have  ac- 
cess to  the  New  York  State  Geological  Reports  will  find  in  Vol. 
IV,  plate  VII,  a  better  proportioned  drawing  of  the  above  profile; 
but  it  is  ten  feet  long.) 

You  ought  to  take  a  great  deal  of  exercise  on  the  geological 
map,  and  especially  in  the  construction  of  sections.  No  matter 
if  it  requires  two  or  three  days  to  finish  one  study. 

Let  us  construct  a  section  or  profile  from  Nashville  to  Savan- 
nah. Here  it  is  (Fig.  54).  You  will  notice  that  the  Cambrian  east 
of  Nashville  is  not  known  to  be  overlaid  by  Silurian;  and  when 
we  trace  it  to  the  east  of  the  Appalachians  it  is  so  metamorphosed 
that  we  are  unable  to  say  whether  the  formation  is  Cambrian  or 
Silurian,  and  so  it  is  simply  put  down  on  the  map  as  Cambro-silu- 


THERMAL   WATERS. 


129 


rian.  After  passing  the  dome  of  the  Eozoic,  we  find  it  overlaid 
directly  by  Tertiary  strata,  and  we  must  so  represent  it.  Not  un- 
likely, however,  some  strata,  intermediate  in  age  between  Eozoic 
and  Tertiary  would  be  found  beneath  the  Tertiary  if  we  could 
make  exploration.  The  Tertiary  passes  under  the  waters  of  the 
Atlantic. 


FIG.  54.— SECTION  FROM  NASHVILLE  TO  SAVANNAH  AND  THE  ATLANTIC  OCEAN. 

EXERCISES. 

Construct  sections  as  follows:  From  Madison,  Wis.,  to  Chicago.  From 
Chicago  to  St.  Louis.  From  Sandusky,  Ohio,  to  Nashville,  Tenn.  From 
Mackinac  to  Cincinnati.  From  Montreal  to  Albany.  From  N.ew  York  city 
to  Oswego.  From  St.  Louis  to  Cincinnati.  From  Cincinnati  to  Newbern, 
N.  C.  From  St.  Paul  to  Chicago.  From  Cairo,  111.,  to  Cincinnati.  From 
Kingston,  Ont.,  to  Chicago.  From  Detroit  to  Fortress  Monroe.  From 
Cleveland  to  Cincinnati,  and  thence  down  the  Ohio  to  its  mouth.  The  stu- 
dent may  also  inspect  the  section,  Fig.  33,  and  see  whether  it  agrees  with  the 
geological  map. 


STUDY  XXII.—  Thermal  Waters. 

Everyone  is  familiar  with  the  diurnal  influence  of  the  sun's 
rays  on  the  earth's  surface  temperature;  and  every  one  has  no- 
ticed that  at  night  the  surface  cools  to  some  extent.  These  diur- 
nal fluctuations  of  temperature  diminish  downward  in  amount, 
and  at  the  depth  of  about  thirty-two  inches  disappear  altogether. 
But  there  are  also  seasonal  fluctuations,  and  these  can  be  traced 
to  a  depth  of  about  fifty  feet.  The  depth,  however,  varies  with  the 
amount  of  the  seasonal  fluctuation.  It  would  be  less,  for  instance, 
in  Florida  than  in  Manitoba.  But  we  may  assume  fifty  feet  for  a 
mean.  This  implies  that  a  thermometer  buried  at  that  depth 
would  indicate  a  constant  temperature  throughout  the  year. 


130  GEOLOGICAL   STUDIES. 

Just  above  this  depth  the  influence  of  summer  would  produce  a 
slight  rise,  and  the  influence  of  winter  a  slight  depression.  But 
the  winter  and  summer  influences  are  each  about  a  year  in  reach- 
ing this  depth  and  dying  out.  Each  is  about  six  months  in 
reaching  a  depth  of  twenty-five  feet.  That  is,  the  July  influence 
is  felt  in  January  at  a  depth  of  twenty-five  feet;  and  the  January 
influence  is  felt  in  July  at  the  same  depth.  Accordingly,  water 
from  a  well  of  this  depth  might  really  be  colder  in  summer  than 
in  winter. 

If  we  carry  our  thermometer  below  the  depth  of  fluctuating 
temperature, —  that  is,  below  about  fifty  feet  —  we  find  the  tem- 
perature of  the  earth  continually  higher.  We  experience  this  in 
mining  operations,  where  the  temperature  sometimes  reaches 

J5 


FIG.  55.— AN  ARTESIAN  WELL  AT  CHICAGO. 

Ci  Chicago.  B,  Baraboo,  Wis.  E,  Eozoic  Quartzite.  P,  Potsdam  Sandstone.  Jf,  Lower 
Maguesian  Limestone.  S,  St.  Peter's  Sandstone.  T,  Trenton  and  Galena  Lime- 
stones. JV,  Niagara  Limestone.  (See  Fig.  39.) 

eighty  or  one  hundred  degrees,  or  even  more;  and  work  would  be 
impossible  without  means  for  introducing  air  from  above.  We 
experience  it  in  tunnelling  mountains,  as  Mont  Cenis  and  Mont 
St.  Gothard.  We  observe  it  in  the  temperatures  of  the  water  of 
artesian  wells.  These  are  wells  bored  down  to  some  porous  and 
water-bearing  stratum,  whose  outcrop  is  some  distance  away  at  a 
higher  level  than  the  place  of  boring.  In  general,  for  such 
depths  as  we  have  been  able  to  reach,  the  temperature  averages 
about  one  degree  higher  for  every  fifty-one  feet  of  descent.  The 
deepest  artesian  well  ever  bored  is  at  Sperenberg,  near  Berlin, 
Prussia.  Its  depth  is  4,172  English  feet  (4,042  Flemish),  and  the 
bottom  temperature  is  118°  Fahrenheit  (38°.25  Reaumur).  As 
the  temperature  at  fifty  feet  was  54°. 74  Fahrenheit,  the  mean 
rate  of  increase  was  one  degree  for  sixty-five  feet  of  descent. 


THERMAL    WATERS. 


131 


There  seemed  to  be  a  diminishing  rate  of  increase  at  the  greater 
depths.  Indeed,  it  can  hardly  be  considered  probable  that  a  con- 
stant rate  should  continue  indefinitely.  At  an  assumed  rate  of 
one  degree  for  fifty-one  feet,  it  is  easy  to  calculate  at  what  depth 
the  temperature  of  boiling  water  would  be  reached,  knowing  the 
mean  annual  temperature  of  the  place.  But  it  will  be  borne  in 
mind  that  under  the  pressure  due  to  any  depth  beneath  the  sur- 
face, water  would  retain  its  liquid  state  at  temperatures  above 
212°.  At  a  pressure  of  ten  pounds  to  the  square  inch  above 
atmospheric  pressure,  the  boiling  temperature  is  about  239°. 

Now,  it  may  be  inferred  from  what  we  have  already  observed 
and  reasoned,  that  many  strata  w7hich  present  their  edges  at  the 
surface,  extend  down  to  the  depth  of  hundreds  or  thousands  of 
feet.  This  may  be  concluded,  even  from  Fig.  41,  or  better  from 
Fig.  46,  where  an  artesian  well  is  shown  starting  in  Lower  Jurassic 
strata  and  reaching  a  water-bearing  stratum  in  the  Upper  Carbon- 
iferous. Surface  water  following  the  course  of  such  a  stratum,  a, 
Fig.  56,  would  become  heated.  If  at  such  depth  a  fault  or  frac- 
ture of  the  crust  should  be  encountered,  the  water  might  rise  to 
the  surface  by  hydrostatic  pressure,  precisely  as  through  an  arte- 
sian boring;  and  thus  a  warm  spring  would  result,  as  shown  in 
Fig.  56.  In  the 
case  of  the  springs 
at  Bath,  England, 
a  is  in  the  Mendip 
Hills,  the  temper- 
ature of  the  water 
is  120°,  and  the 
depth  of  JB  must 

be       about      3,500  FlG   56._GEOLOGT  OF  A  WAKM  SPRING. 

feet,    the    mean    of  a,  porous  stratum  receiving  water  at  the  surface,  and  inter- 

,          i .                ,  cepted  by  a  fault  at  5,  at  such  depth  that  the  temperature 

!ln&  of  the  water  is  over  100°,  whence  it  rises  along  the  fissure, 

50°.       Many    warm  and  forms  a  warm  spring  at  S.    a'  continuation  cf  a. 

and     hot     springs 

undoubtedly  result  in  this  way.     In  other  places,  as  at  Tuscan 

Springs,  Cal.,  no  faulting  of  the  strata  exists.     Here,  Fig.  57, 


132 


GEOLOGICAL   STUDIES. 


the  Cretaceous  strata  simply  present  an  anticlinal  and  a  fracture 
through  which  the  water  rises  from  such  depth  as  to  have  been 
heated.  The  steep  dip  of  the  Cretaceous  sandstone  would  soon 
reach  the  requisite  depth.  From  that  they  rise  eastward,  and 


FIG.  57.— SECTION  AT  TUSCAN  SPRINGS,  SACRAMENTO  VALLEY,  CAL.    (Whitney.) 

a,  a,  Basaltic  Lava;  0,  &,  Volcanic  Ash  and  Scoriae;  c,  c,  Conglomerate;  d,  c?,  Cretaceous 

Sandstone;  s,  Springs. 

come  to  the  surface  along  the  ancient  shore  of  the  Cretaceous 
ocean   which   bathed  the  western  flanks   of  the  Sierra  Nevada. 
Along  that  outcrop  the  supply  of  water  is  probably  received. 
The  water  of  hot  springs  has  great  solvent  power,  and  thus, 


FIG.  58.— NATURAL  BRIDGE  OF  TRAVERTIN  FORMED  BY  AN  INCRUSTING  SPRING  AT 
CLERMONT,  FRANCE.    (Scrope.) 

very  frequently,  the  spring  delivers  mineral  water.  Calcium 
carbonate  and  silica  are  thus  very  often  brought  to  the  surface. 
As  the  water  cools,  much  of  the  mineral  matter  is  precipitated  on 
the  surfaces  over  which  it  flows,  and  we  get  deposits  of  tufa  or 


THERMAL   WATERS. 


133 


sinter.  Relief  of  the  pressure  tends  also  to  cause  the  water  to 
give  up  a  portion  of  its  mineral,  precisely  as  in  the  case  of  com- 
mon springs,  which  we  considered  in  Study  II.  These  tufaceous 
deposits  sometimes  acquire  enormous  extent. 

In  more  numerous  cases  warm  springs  are  found  in  proximity 
to  volcanoes.  In  central  France,  especially  in  the  departments  of 
Cantal,  Haute  Loire,  and  Puy  de  Dome,  is  a  district  of  extinct 


FIG.  59.— BASINS  AT  MAMMOTH  HOT  SPRINGS  OF  GAKDINER'S  RIVER,  YELLOWSTONE 
NATIONAL  PARK.    (Peale.) 

volcanoes,  and  here  the  phenomena  of  warm  springs  and  their 
deposits  are  developed 'on  a  vast  scale.  At  Clermont  the  deposits 
from  a  calcareous  spring  have  formed  an  elevated  natural  aqueduct 
two  hundred  and  forty  feet  in  length,  and  terminating  in  an  arch 
thrown  across  the  stream  it  originally  flowed  into,  sixteen  feet 
high  and  twelve  feet  wide.  (See  Fig.  58.)  Very  extensive 
deposits  occur  in  Italy  and  other  European  countries;  but  the 
most  remarkable  are  found  in  the  Yellowstone  National  Park, 


134  GEOLOGICAL   STUDIES. 

where  Peale  enumerates  2,195  hot  springs.  These  springs  are 
also  located  in  a  volcanic  district.  In  Fig.  59  is  given,  from 
Hayden's  report  for  1878,  a  view  of  a  group  of  these  springs 
which  have  built  a  curious  series  of  basins.  Very  similar  effects 
are  produced  by  the  thermal  springs  of  New  Zealand,  Asia 
Minor,  and  other  regions. 

Many  of  the  springs  of  the  National  Park  present  the  phe- 
nomena of  geyser  action,  or  periodic  ejection  of  hot  water  with 
great  force,  sufficient  in  some  cases  to  throw  it  to  the  height  of 
one  or  two  hundred  feet.  Peale  enumerates  seventy-one  geysers. 
In  Fig.  60  is  presented  a  view  of  the  "Giant  Geyser"  in  action. 
The  crater  has  been  formed  by  deposition  of  a  mineral  known  as 
geyserite.  It  rises  ten  feet  above  the  platform,  and  at  base  meas- 
ures twenty-four  feet  by  twenty-five,  diminishing  to  eight  feet  at 
the  top.  Its  depth  is  twenty-five  feet.  The  temperature  of  the 
water  is  about  198°  Fahrenheit.  Its  eruptions  are  some  days 
apart,  but  the  volume  of  water  discharged  is  enormous,  and  the 
altitude  attained  is  two  hundred  to  two  hundred  and  fifty  feet. 
The  power  required  to  produce  this  result  causes  the  earth  to 
tremble,  and  a  deep  rumbling  sound  to  be  emitted.  The  so-called 
geyserite  is,  in  other  words,  a  silicious  sinter.  Silica  is  held  in 
various  proportions  in  these  waters  (from  eight  to  fifty-four  per 
cent),  and  is  thrown  down,  as  Peale  thinks,  in  consequence  of 
evaporation;  but  cooling  and  relief  of  pressure  probably  con- 
spire. 

A  geyser  in  action  is  a  striking  geological  phenomenon,  and 
much  speculation  has  been  had  in  reference  to  its  mechanism. 
The  explanation  which  seems  most  satisfactory  is  that  proposed 
by  Bunsen.  The  water  accumulating  in  the  geyser  tube  is  a  long 
column,  probably  more  or  less  tortuous.  It  is  heated  below,  and 
a  tendency  to  equalization  of  temperature  throughout  exists 
through  the  means  of  a  circulation;  but  the  difficulties  of  circu- 
lation cause  always  a  higher  temperature  at  the  bottom.  After  a 
time  the  bottom  temperature  exceeds  the  boiling  temperature  at 
the  top,  but  the  bottom  water  does  not  boil  because  the  pressure 
is  increased.  At  the  depth  of  thirty-three  feet  the  pressure  is 


THERMAL    WATERS. 


135 


FIG.  60.— GIANT  GEYSER  IN  ACTION.    UPPER  GEYSER  BASIN,  FIRE  HOLE  RIVER, 
YELLOWSTONE  NATIONAL  PARK.    (Peale.) 


136 


GEOLOGICAL   STUDIES. 


two  atmospheres,  and  the  boiling  temperature  250°.  But  by-and- 
by  the  increase  of  heat  below  brings  the  water  to  the  boiling  tem- 
perature; or  in  some  cases  a  momentary  relief  of  the  pressure 
makes  the  existing  temperature  a  boiling  temperature.  Then 
steam  is  instantly  formed,  and  the  column  of  water  above  is 
thrown  out. 

A   somewhat  simpler  explanation  is   suggested  by  the  well 


FIG.  61.— GEYSERITES.    FROM  UPPER  AND  LOWER  FIRE  HOLE  BASIN.    (Peale.) 

known  behavior  of  water  and  steam  when  attempting  to  circu- 
late through  the  same  pipe,  and  by  the  analogous  case  of  water 
and  gas  in  one  of  the  spouting  wells  of  an  oil  district.  Water 
simply  accumulates  in  the  geyser  pipe  upon  the  steam  formed  in 
the  lower  part  by  the  bottom  temperature.  The  steam  for  a  time 
is  subjected  to  compression,  and  the  compression  (condensation) 
increases  with  the  continued  development  of  steam.  Finally,  the 
elastic  force  becomes  sufficient  to  lift  the  column  of  water.  The 


THERMAL   WATERS.  137 

commencement  of  escape  now  diminishes  pressure,  and  a  large 
volume  of  steam  is  instantly  formed,  which  causes  the  violent 
action.  The  heavy  thumps  sometimes  heard  before  and  during 
the  action  are  due  to  collapses  of  steam  in  contact  with  the  water, 
and  are  strictly  the  same  in  principle  as  the  sharper  sounds  fre- 
quently heard  in  the  steam  pipes  employed  for  warming  buildings. 

EXERCISES. 

The  artesian  well  at  the  insane  asylum,  St.  Louis,  was  3,843!  feet  deep, 
the  temperature  of  the  water  105°,  and  the  mean  annual  temperature  at  the 
surface  55°;  what  is  the  rate  of  increase  of  temperature?  The  correspond- 
ing data  at  Charleston,  S.  C.,  were  1,250  feet,  87°,  and  66°;  what  is  the  rate 
of  increase?  Make  the  calculation  for  any  other  well  of  which  you  can  get 
the  data.  At  what  date  will  the  temperature  of  July  1  be  felt  at  the  depth 
of  twelve  feet?  If  winter  cold  begins  at  Christmas,  at  what  date  will  it  pen- 
etrate through  the  ground  to  the  bottom  of  a  cellar  five  feet  deep?  Will  the 
whole  severity  of  the  surface  cold  be  felt  at  that  depth?  What  should  be  the 
temperature  of  water  from  the  bottom  of  a  well  one  hundred  feet  deep  at  a 
spot  where  the  annual  mean  is  40°?  If  the  flow  of  water  in  this  well  comes 
from  below,  will  its  temperature  be  higher  or  lower  than  your  calculation? 
How  do  we  measure  the  temperature  of  the  water  in  the  bottom  of  an  arte- 
sian well?  Why  can  we  not  be  sure  the  temperature  there  taken  is  the  true 
temperature  due  to  that  depth  ?  If  the  strata  bored  through  have  a  steep 
dip,  is  the  water  likely  to  have  come  from  a  higher  or  a  lower  level?  How 
would  this  affect  the  temperature?  And  would  this  wrong  temperature  affect 
your  calculation  of  the  rate  of  increase  of  temperature?  What  is  the  differ- 
ence between  an  artesian  well  and  a  warm  spring?  If  the  temperature  of  a 
spring  in  central  Arkansas  is  100°,  from  what  depth  should  the  water  rise? 
If  the  temperature  of  the  Giant  Geyser  is  198°,  what  is  the  length  of  its  fun- 
nel—  taking  no  account  of  the  elevation  above  the  sea?  Does  this  tempera- 
ture of  198°  indicate  accurately  the  temperature  at  the  bottom  of  the  funnel? 
If  not,  why  not?  .How  does  the  discrepancy  affect  the  result  of  your  calcu- 
lation? How  many  atmospheres  of  pressure  at  the  depth  resulting  from 
your  calculation?  Try  to  ascertain  at  what  temperature  steam  forms  under 
such  pressure.  Suppose  the  temperature  of  the  water  is  240°  and  the  press- 
ure two  atmospheres,  will  the  water  boil  ?  Suppose  now  the  pressure  is  sud- 
denly diminished  to  one  and  a  half  atmospheres,  what  would  happen?  Why 
do  warm  springs  deposit  calcareous  matter,  and  geysers  silicious  matter?  Is 
the  silicious  matter  the  cause  of  the  geyser  mode  of  outflow  ? 


138  GEOLOGICAL   STUDIES. 

STUDY  XXIII.  —  Volcanoes. 

We  have  ascertained,  from  observations  made,  that  the  inter- 
nal temperature  of  the  earth  rises  as  we  descend  below  the  zone 
of  uniform  temperature,  and  to  this  fact  we  have  not  hesitated  to 
ascribe  the  heat  of  thermal  waters.  We  have  no  reason  to  doubt 
that  the  heat  continues  to  rise  beyond  the  possibility  of  the  exist- 
ence of  water,  and  even  till  the  temperature  is  sufficiently  high 
to  fuse  mineral  substances.  This  is  an  inference;  but  it  is  easy 
to  subject  it  to  the  test  of  observation.  Visitors  to  Naples,  in 
Italy,  tell  us  that  in  the  immediate  vicinity  rises  a  mountain  4,000 
feet  above  the  bay,  which  is  seen  frequently  to  emit  a  volume  of 
steam  and  smoke,  as  if  its  summit  were  a  chimney,  and  a  great 
fire  were  nursed  within  the  mountain.  This  is  Vesuvius.  They 
tell  us  that  the  surface  of  the  mountain  is  completely  covered 
with  ragged  masses  and  scraps  of  rocks  quite  unlike  any  with 
which  we  are  familiar,  being  dark,  compact,  fine,  often  glassy,  in 
many  cases  coarsely  cellular  and  light,  and  having  much  the  ap- 
pearance of  slags  from  iron  and  copper  furnaces.  We  may  easily 
ascertain  from  the  testimony  of  eye-witnesses  that  these  slags 
have  been  ejected,  in  a  molten  state,  from  the  chimney  of  the 
mountain,  and  that  sometimes  copious  streams  of  molten  matter 
have  burst  through  fissures  and  flowed  down  the  mountain  side. 
These  outflows  are  accompanied  by  volumes  of  aqueous  vapor 
and  gases  and  acid  fumes,  which  rise  in  a  vertical  column  through 
the  crater  to  the  height  of  several  thousand  feet  —  in  1779,  ten 
thousand  feet,  according  to  Sir  William  Hamilton.  Accompany- 
ing these  are  stones  and  ashes,  sometimes  in  great  abundance. 
The  aqueous  vapors  condense  in  the  upper  air  and  form  clouds, 
illuminated  by  the  glowing  lava  and  by  the  lightnings  generated 
in  the  bosom  of  the  vapor.  Torrents  of  rain  sometimes  descend, 
converting  the  ashes  into  mud,  and  burying  the  surface  of  the 
earth  for  many  miles  around.  There  are  records,  indeed,  of  very 
destructive  eruptions.  One  which  occurred  in  the  year  79  buried 
three  cities  —  Pornpeii,  Herculaneum,  and  Stabiae  —  arid  the  work 
of  excavating  them  is  now  in  progress  (Fig.  63). 


VOLCANOES. 


139 


FIG.  G2.— MT.  VESUVIUS  AND  THE  BAY  OP  NAPLES.    (Palmieri.) 


140 


GEOLOGICAL   STUDIES. 


Vesuvius  and  ^Etna  are  the  two  classical  volcanoes  of  Eu- 
rope; but  many  other  evidences  of  the  existence  of  internal 

fires  are  revealed  in 
the  volcanic  activities 
of  the  Lipari  Islands, 
in  the  fumaroles  and 
solfataras  of  the  vol- 
canic districts,  and  in 
the  occasional  out- 
burst of  a  volcanic 
island  from  the  bot- 
tom of  the  Mediterra- 
nean. A  fiimarole 
is  an  escape  of  steam 
from  the  ground. 
When  accompanied 
by  sulphur  vapors  and 
other  gases  it  is  a  sol- 
fatara.  Fumaroles 
are  numerous  in  the 
Yellowstone  National 
Park,  as  also  in  most 
volcanic  regions. 

Let  us  listen  to  a  statement  of  what  occurred  on  ^Etna  in 
1865.  This  volcano,  according  to  the  government  survey,  is 
10,868  feet  high,  and  its  sides  slope  at  an  angle  of  six  to  eight 
degrees.  Its  crater  is  a  vast  abyss,  nearly  1,000  feet  deep,  and 
two  or  three  miles  in  circumference.  Sometimes  it  is  nearly  full 
of  lava;  at  other  times  it  appears  to  be  bottomless.  In  July, 
1863,  after  a  series  of  convulsive  movements,  a  fissure  opened  on 
the  south  side  of  the  loftiest  cone,  and  molten  matter  began 
slowly  to  issue  and  descend.  Masses  of  lava  and  ashes  were  at 
the  same  time  ejected  from  the  mouth  of  the  crater.  For  eigh- 
teen months  the  mountain  threatened  some  ulterior  convulsion. 
Molten  lava  rose  in  the  crater  and  illuminated  the  skies.  Evi- 
dently it  pressed  with  enormous  force  against  its  walls,  and  these 


FIG.  63.— THE  EXCAVATION  OF  POMPEII,  BURIED  IN  AN 
ERUPTION  or  VESUVIUS.  Via  Stabiae,  new  quarter. 
(Photograph.) 


VOLCANOES. 


141 


were  continually  weakened  by  melting  away.  At  length,  on  the 
night  of  the  30th  of  January,  1865,  the  walls  yielded,  and  a  rent 
opened  a  mile  and  a  half  in  length  on  the  north  of  Monte  Fru- 
mento,  one  of  the  secondary  cones  rising  on  the  slope  of  ./Etna. 


3  4  5 

FIG.  64.— MAP  OF  ^ETNA  AND  ITS  ERUPTIONS.    (After  S.  von  Waltershausen.) 
1,  Ancient  Lava;  2,  Lavas  of  the  Middle  Ages;  3,  Lava  of  1669;  4,  Lavas  of  1852  and  1865; 
5,  Lava  of  1879;  6,  Recent  Lavas ;   7,  Cones  and  Craters ;  8,  Non- Volcanic  Rocks.    A, 
Aci  Reale ;  B,  Val  del  Bove ;  C,  Catania ;  R,  Randazzo ;  S,  River  Simeto. 

From  this  molten  lava  issued  for  some  hours,  when  communica- 
tion with  the  interior  supplies  seems  to  have  been  obstructed. 
On  the  following  day,  new  eruptions  from  the  fissure  took  place, 


142  GEOLOGICAL   STUDIES. 

and  six  principal  cones,  formed  of  ejected  matter,  were  raised. 
These  gradually  blended  together,  absorbing  smaller  cones,  until 
a  height  of  nearly  300  feet  had  been  reached.  The  liquid  lava 
issued  from  the  lower  craters,  while  the  upper  belched  forth  only 
stones  and  ashes.  In  two  months  the  cone  nearest  to  Frumento 
seemed  to  have  become  choked  up,  and  only  emitted  sulphurous 
and  hydrochloric  vapors.  The  cone  next  lower  continued  to 
eject  periodically,  and  with  loud  explosions,  volumes  of  vapor, 
ashes,  and  stones;  while  the  lowest  cones  continued  to  rumble 
and  discharge  molten  matter.  By  degrees  the  violence  of  the 
action  abated.  At  first  the  erupted  matter  rose  5,500  to  5,800 
feet;  then  it  fell  to  300,  and  gradually  ceased  to  escape. 

During  the  first  six  days,  the  amount  of  matter  escaping  from 
the  fissure,  according  to  Sylvestri,  was  about  117  cubic  yards  a 
second  —  equivalent  to  a  volume  twice  the  size  of  the  Seine  at 
low  water.  Near  the  outlet  it  flowed  twenty  feet  a  minute; 
lower  down,  spreading  over  a  wider  surface,  its  speed  was  one 
and  a  half  to  six  feet  a  minute.  On  the  second  of  February  the 
principal  stream,  now  900  to  1,650  feet  broad  and  forty-nine  feet 
deep,  reached  an  escarpment  three  miles  from  the  fissure,  over 
which  it  plunged,  a  cataract  of  fire,  into  the  gorge  below.  This 
spectacle  was  ended  in  a  few  days  by  the  wearing  down  of  the 
ledge  and  the  filling  of  the  ravine  to  the  depth  of  160  feet.  From 
this  the  river  of  fire  continued,  and  by  the  middle  of  February  it 
was  more  than  six  miles  long,  well  incrusted  with  cooled  lava,  and 
making  but  slow  progress.  Farm  houses  were  swept  away,  and 
pastures  and  cultivated  grounds  were  buried  beneath  slowly 
hardening  rock.  Entering  the  ancient  forest,  it  swept  down 
100,000  to  130,000  trees,  and  the  burning  trunks  floated  along 
upon  the  moving  stream.  Some  months  after  the  commence- 
ment of  the  eruption,  the  interior  of  the  stream  of  lava  was  still 
incandescent  and  moving.  Continually  the  crust  was  burst  by  the 
pressure  from  behind;  new  rills  would  start  and  freeze,  and  frag- 
ments of  the  crust  became  implanted  in  the  new  rock,  so  that  the 
exterior  was  roughened  by  innumerable  sharp  edged  projections. 

Fearful  as  was  this  eruption,  it  was  insignificant  compared 


YOLCANOES.  143 

with  former  ones.  Since  this  date  the  mountain  has  been  quiet; 
but  during  twenty  centuries,  seventy-eight  eruptions  have  been 
recorded  —  the  first  in  the  seventh  century  B.C.,  in  the  time  of 
Pythagoras.  (See  Fig.  64.)  In  some  of  them  the  flows  of  lava 
have  been  more  than  fifteen  miles  in  length,  and  have  covered 
areas  of  more  than  forty  square  miles  (eruption  of  1669),  which 
were  once  in  a  perfect  state  of  cultivation,  and  dotted  over  with 
towns  and  villages.  The  evidences  are  seen  in  the  lava  patches 
which  still  rest  on  the  mountain  slopes.  In  1669  a  stream  of 
lava  poured  over  the  walls  of  Catania,  sixty  feet  in  height,  and 
overwhelmed  a  part  of  the  city.  In  1693  an  earthquake  accom- 
panied, which  destroyed  60,000  to  100,000  inhabitants,  of  whom 
18,000  were  Catanians.  In  1755  a  flood  of  water,  estimated  at 
16,000,000  cubic  feet,  descended  the  Val  del  Bove,  carrying  all 
before  it.  In  former  days,  thousands  of  other  lava  flows  and 
cones  of  ashes  have  added  their  contributions  to  the  mass  of  the 
volcano,  so  that  there  is  no  spot  which  has  not,  sooner  or  later, 
been  covered  by  the  depositions.  In  fact,  the  evidence  is  that 
the  total  bulk  of  ^Etna,  from  summit  to  base,  down  even  to  the 
lowest  submarine  depths,  is  nothing  but  the  product  of  suc- 
cessive eruptions  of  molten  lava,  ashes  and  cinders. 

From  all  observations  made,  it  appears  that  the  usual  tenor 
of  events  attending  an  eruption  of  ^Etna  is  as  follows:  Earth- 
quakes are  the  premonitory  symptoms;  loud  explosions  are  heard; 
rifts  open  in  the  side  of  the  mountain;  smoke,  sand,  ashes  and 
scoriae:  are  discharged;  the  action  localizes  itself  in  one  or  more 
craters;  cinders  are  thrown  out,  and  accumulate  around  the 
crater  in  a  conical  form;  ultimately,  lava  rises  through  the  new 
cone,  frequently  breaking  down  one  side  of  it,  where  there  is 
least  resistance,  and  flowing  over  the  surrounding  country.  Then 
the  eruption  is  at  an  end. 

Could  we,  with  Captain  Button,  visit  Hawaii,  we  should  find 
the  conditions  varied,  but  essentially  the  same.  This  island  is 
composed  mainly  of  three  volcanic  mountains,  Loa,  Ke"a,  and 
Hualalai  [give  European  sounds  to  the  vowels]  7,822  feet  high. 
Mauna  Loa  is  13,760  feet  in  height,  and  has,  besides  its  summit 


144 


GEOLOGICAL    STUDIES. 


crater,  another  one,  Kilauea,  3,970  feet  above  the  sea  level. 
This  is  a  type  of  vent  so  unlike  ordinary  craters  that  Button 
proposes  for  it  the  new  name  caldera.  The  eruptions  of  Loa  are 


FIG.  65.— MAP  or  HAWAII,  SHOWING  LAVA  FLOWS.    (Dutton.)    H,  Hilo;  H  U,  Hualalai; 
K,  Kilauea;  K E,  Mauna  Kea ;  K  0,  Kohala  Mts.    L,  Mauna  Loa. 

quiet.     The  first  indication  is  a  light  sent  from  the  crater  to  the 
clouds.     The  liquid  lava  rises  in  the  crater;  sometimes  it  over- 

Hualalai    M.  Loa 


FIG.  66.— PROFILE  OF  HAWAII  THROUGH  HUALALAI  AND  MAUNA  LOA,  PROM  N.  W.  TO  S.  E. 
Distance  30  miles.    Section  extends  18,000  ft.  below  sea  level.    (Dutton.) 

flows,  but  generally  a  fissure  opens  on  the  side,  and  the  lava 
pours  forth,  accompanied  by  ejections  of  stones,  cinders,  and 
ashes.  The  stream  of  lava  has  been  known  to  flow  sixty  miles, 


VOLCANOES.  145 

and  at  times  it  has  reached  the  sea.  Lava  streams  of  various 
dates  are  shown  in  Fig.  65.  The  eruptions  at  the  summit  crater 
are  not  generally  accompanied  by  disturbances  in  Kilaue"a.  The 
converse  is  equally  true.  Kilauea  is  a  crater  or  caldera  16,000 
feet  long,  seven  and  one-half  miles  in  circuit,  nearly  four  square 
miles  in  area,  and  600  feet  deep.  The  floor  is  of  cooled  lava, 
with  one  or  more  pits  of  molten  lava  continually  in  a  state  of 
agitation,  and  at  times  overflowing  the  brim  and  flooding  the 
solid  floor.  Mauna  Kea  seems  to  be  extinct.  On  the  island  of 
Maui,  the  volcano  Haleakala  is  10,217  feet  high,  with  a  crater 
2,000  feet  deep;  and  lava-flooded  valleys  one  to  two  miles  wide 
lead  from  it  toward  the  sea. 

The  red  sunsets  of  1883  and  1884  are  well  remembered  by 
all.  It  seems,  at  first  view,  very  far-fetched  to  assume  any  con- 
nection between  them  and  volcanic  activities  ;  but  the  opinion 
prevails  very  generally  that  they  were  caused  by  the  fine  ashes 
ejected  on  the  26th,  27th,  and  28th  of  August,  1883,  from  a  vol- 
cano on  a  small  island  lying  in  the  Strait  of  Sunda,  and  com- 
monly known  as  Kra-kat'oa.  There  were  three  volcanic  summits 
on  the  island.  The  northern  and  lowest,  Perboewatan,  began  to 
be  active  in  May,  after  a  rest  of  two  centuries;  the  middle  sum- 
mit, Danan,  was  the  seat  of  the  great  eruption  of  1883,  while 
the  southern  and  highest  summit,  Ra-ka'ta,  eight  hundred  and 
twenty-two  metres,  did  not  suffer.  The  eruption  was  accompa- 
nied by  several  terrific  explosions,  the  greatest  of  which  occurred 
at  five  minutes  past  10  A.M.,  August  27,  Batavia  time.  These  air 
shocks  travelled  no  less  than  three  and  one-fourth  times  around 
the  earth.  The  sounds  were  heard  over  an  area  whose  radius  is 
30°,  or  3,333  kilometres,  or  whose  diameter  would  reach  from  the 
Canary  Islands  to  Jerusalem,  and  from  Novaya  Zemlia  to  the  mid- 
dle of  the  Soudan.  The  matter  ejected  is  estimated  at  eighteen 
cubic  kilometres;  and  within  a  circle  of  fifteen  kilometres'  radius 
the  thickness  of  the  layers  deposited  was  twenty  to  forty  metres 
—  at  the  base  of  the  mountain,  sixty  to  eighty  metres.  The  finer 
ashes  fell  1,200  kilometres  away,  and  the  finest  seem  to  have 
floated  for  months  in  the  upper  air.  The  steam-cloud  was  seen  to 


146 


GEOLOGICAL   STUDIES. 


rise  11,000  metres.     The  high  southern  peak  was  split  through 
the  middle,  and  the  northern  half,  together  with  the  other  two 


FIG.  67.— FORM  OF  THE  SUMMIT  or  VESUVIUS,  IN  1756,  SHOWING  FOUR  CRATERS.  (Scrope.) 

mountains,  sank  out  of  sight.  The  soundings  over  it  are  now 
200  to  300  metres.  The  size  of  the  island  was  formerly  thirty- 
three  and  one-half  square  kilometres;  of  this  only  ten  square 
kilometres  remain,  but  the  volcanic  depositions  have  added  five 
square  kilometres. 

The  explosive  sounds,  the  atmospheric  shocks,  and  the  great 
sea  waves  which  destroyed  more  than  35,000  lives,  are  believed 
to  be  due  to  the  falling  in  of  the  crater  at  successive  intervals. 
This  is  a  common  incident  of  volcanic  eruptions.  The  present 

crater  of  Vesuvius  rises 
within  a  much  larger 
crater,  Somma,  which 
resulted  from  the  en- 
gulfment  of  a  former 
crater  during  an  erup- 
tion. In  1756  the  sum- 


mit presented  the  ap- 

pearance  shown  in  Fig. 

FIG.  68.— TRIPLE  CRATER  or  THE  TJOENDOENG  VOL-       *  TT  . 

CANO,  SUMATRA.    (Hochstetter.)  67.     Here  were  the  re- 

mains of  four  craters, 

one  within  another.     The  phenomena  of  the  Sundanese  volcanoes 
illustrate  the  same  thing,  as  shown  in  Figs.  68  and  69.     This  is 


VOLCANOES. 


147 


explained  by  Hochstetter  on  the  supposition  of  a  vast  exca- 
vation in  the  moun- 
tain, as  shown  in  Fig. 
70.  By-and-by  the 
arch  becomes  too 
weak  to  support  its 
weight,  and,  falling 


FIG.  69.— QUADRUPLE  CRATER  OP  MERAPI  (SUMATRA). 
(Hochstetter.) 


into  the  abyss,  leaves  the  circle  of  breakage  to  contribute  the 


FIG.  70.— VOLCANIC  CONE,  WITH  INTERIOR  MELTED  AWAY.    (Hochstetter.) 

rim  of  a  new  and  larger  crater,  as  shown  in  Fig.  71.     Then,  after 
a  period  of  quiescence,  the  liquid  pool  freezes  over,  arid  a  new 
and    small    crater,    on 
occasion  of  subsequent 
activity,  begins  to  grow 
in  the  centre. 

Visitors  to  California 
and  Oregon  are  greatly 
interested  in  the  grace- 
ful forms  of  the  vol- 
canic peaks  of  the  Si- 
erra Nevada  and  Cascade  ranges.  Most  admired  of  all  is  Mt. 
Shasta,  rising  a  solitary  and  shapely  cone  14,440  feet  above  the 
sea  (Whitney).  It  has  ceased  to  be  active,  but  the  evidences  of 
great  former  activity  appear  in  enormous  sheets  of  volcanic  ma- 
terial covering  the  country  around.  The  fires  of  Mt.  Hood,  in 
Oregon,  appear  to  be  dying  out,  only  moderate  heat  and  vapors 
escaping  to  the  top.  But  in  times  past  it  has  covered  many  hun- 


FIG.  71.— VOLCANIC  CONE,  AFTER  THE  FALLING- IN  op 
THE  CRATER.    (Hochstetter.) 


148  GEOLOGICAL   STUDIES. 

dred  square  miles  with  its  ejections.  The  Columbia  River  has 
cut  through  these  in  a  chasm  4,000  feet  deep.  Mt.  Ranier,  in 
the  same  range,  is  14,444  feet  high.  Its  snow-white  summit  pre- 
sents a  magnificent  spectacle  from  Seattle,  seventy  miles  distant, 
on  Puget  Sound. 

In  many  portions  of  the  trans-Mississippi  region  the  evi- 
dences of  former  volcanic  activity  are  abundant.  The  whole 
Nevada  range,  from  Lassen's  Peak  to  Shasta,  is  volcanic,  and 
so  is  the  Cascade  range,  further  north.  Numerous  series  of  vol- 
canic cones  stretch  along  the  western  slope  of  the  Sierra. 
Near  Mono  Lake  is  a  group  extending  far  south,  a  view  of 
which  is  shown  in  Fig.  72.  This  is  a  cluster  of  truncated  cones 


FIG.  72  —VOLCANIC  COXES,  NEAR  MONO  LAKE,  CAL.     (Whitney.) 

of  very  steep  sides,  chiefly  covered  with  ashes  and  other  loose 
materials,  and  having  numerous  rocky  projections  rising  from 
their  broadly  truncated  tops.  They  reach  the  altitude  of  9,200 
and  9,300  feet  above  sea  level. 

Extinct  volcanoes  are  known  in  many  countries,  but  the  most 
celebrated  region  is  central  France.  Here  hundreds  of  cones 
and  enormous  sheets  of  ejected  material,  worn,  in  later  times, 
by  the  agencies  of  erosion,  have  given  to  a  wide  region  an  aspect 
entirely  unique  and  full  of  interest  to  the  geologist.  Here  is 
subjoined  a  view  taken  from  the  work  of  Poulett  Scrope,  who 
has  studied  and  illustrated  the  region  with  more  detail  and  thor- 
oughness than  any  other  investigator  (Fig.  73). 


VOLCANOES. 


149 


EXERCISES. 

What  is  the  nature  of  the  so-called 
"smoke"  from  volcanoes?  Is  there 
any  "combustion"  in  a  volcano? 
What  is  the  source  of  the  water  which 
issues  as  steam?  What  evidence  can 
you  give  that  this  is  sea  water?  Have 
you  ever  heard  of  mud  ejected  from 
volcanoes?  What  analogy  can  you 
trace  between  volcanoes  and  geysers? 
Enumerate  the  principal  lines  and 
regions  in  which  volcanoes  abound. 
Enumerate  volcanoes  situated  far  in- 
land. Give  some  account  of  any  vol- 
cano not  mentioned  in  the  present 
study.  What  must  be  the  effect  of 
volcanic  action  on  the  internal  heat  of 
the  earth?  If  the  volcanic  cone  is 
formed  of  ejected  materials,  what  is 
under  the  cone?  Do  you  imagine  any 
rocks  of  sedimentary  origin  could  be 
there  ?  Could  granitic  and  other  meta- 
morphic  rocks  be  there?  (See  Fig.  46, 
"trachyte"  and  "basalt.")  Profes- 
sor Whitney  found  masses  of  rose-col- 
ored granite  on  the  tops  of  the  cones 
shown  in  Fig.  72;  how  could  they  be 
accounted  for?  Why  not  consider 
them  bowlders?  Would  it  be  surpris- 
ing to  see  rounded  stones  ejected  from 
a  volcano?  Should  you  see  them, 
where  and  how  would  you  suppose  them 
rounded?  Should  they  afterward  be 
cemented  together,  what  sort  of  a  rock 
would  be  formed?  Have  you  ever 
heard  of  such  a  rock  as  a  fact  ?  Can 
you  suggest  why  the  eruptions  of  ^Etna 
and  Vesuvius  are  attended  by  earth- 
quakes, and  those  of  Mauna  Loa  not? 
Does  it  appear  that  different  volcanoes 
have  an  underground  connection?  Do 


150  GEOLOGICAL   STUDIES. 

the  summit  crater  and  Kilauea  sympathize  together  ?  Do  ^Etna  and  Vesuvius  ? 
Do  Mtua,  and  Stromboli?  Assuming  the  two  craters  of  Mauna  Loa  to  be 
connected,  how  could  lava  stand  in  the  summit  crater,  9,000  feet  higher  than 
Kilauea,  without  escaping  at  Kilauea?  Supposing  the  specific  gravity  of  the 
lava  two  and  eight-tenths,  how  many  atmospheres  of  pressure  would  be  felt 
at  Kilauea? 


STUDY   XXIV.—  Ancient  Lavas. 

The  traveller  returning  southward  from  a  trip  to  Mt.  Shasta 
may  follow  the  broad  valley  of  the  Sacramento  River.  On  his 
left  rise  the  peaks  of  the  Sierra  Nevada,  with  the  foot  hills  in  the 
nearer  distance.  For  a  hundred  miles,  from  Pitt  River  to  Oro- 
ville,  along  the  eastern  side  of  the  Sacramento,  he  traverses  a 
broad  plain  of  volcanic  ashes,  destitute  of  trees  and  almost 
destitute  of  herbage,  and  as  yet  hardly  eroded  into  canons.  On 
nearing  Bear  Creek,  more  solid  lava  makes  its  appearance,  and 
increases  as  he  passes  southward.  This  belt  averages  about 
seventy-five  miles  in  width.  The  materials  may  be  traced  chiefly 
to  the  great  centre  of  eruptive  agency  at  and  near  Lassen's  Peak, 
in  the  Sierra  Nevada.  The  sheets  of  lava  form  a  regular  slope 
from  the  Peak  to  the  Sacramento.  Through  this  the  more  south- 
ern streams  have  sunken  their  channels  five  hundred  to  eight 
hundred  feet  deep.  In  some  situations  crater-bearing  cones  rise 
over  eight  hundred  feet,  and  from  these  have  issued  a  portion  of 
the  materials  which  flooded  the  valley.  These  were  laid  down  on 
Cretaceous  strata.  Tuscan  Springs,  already  mentioned  (Fig.  57), 
are  in  this  region.  The  section  shows  that  the  Cretaceous  strata 
were  somewhat  tilted  before  the  lava  was  poured  out,  and  further 
tilted  since  that  event.  The  conglomerate  is  not  volcanic,  and  its 
presence  implies  the  action  of  a  transporting  agent  over  the  sur- 
face after  the  upheaval  of  the  Cretaceous.  To  this  is  probably  to 
be  attributed  the  erosion  of  the  strata.  This  section  also  shows 
a  breakage  of  the  strata  and  the  escape  of  warm  mineral  waters. 

Near  the  southern  limit  of  this  lava  sheet,  in  the  centre  of 


ANCIENT   LAVAS. 


151 


Butte  county,  the  streams  have  cut 
quite  through  the  lava  into  the  under- 
lying formations,  giving  rise  to  forms 
known  as  "table  mountains."  Here, 
underneath  all,  are  exposed  the  aurifer- 
ous slates,  tilted  up  to  a  steep  north- 
easterly dip,  and  containing  intercalated 
beds  of  Carboniferous  Limestone.  On 
the  upturned  edges  of  these  strata  rest 
nearly  horizontal  Cretaceous  sand- 
stones, with  a  slight  southwesterly  dip. 
Above  these  are  sandstones  interstrati- 
fied  with  shales  containing  leaves  of 
Pliocene  age.  Upon  these  lie  accumu- 
lations of  volcanic  ashes,  scoriae  and 
breccia,  and  over  all  rests  a  heavy  bed 
of  basaltic  lava.  The  section,  Fig.  74, 
is  taken  across  the  general  direction  of 
the  streams,  and  presents,  therefore, 
cuts  across  a  series  of  lava-topped  belts, 
intervening  between  the  streams. 

The  great  auriferous  region  stretch- 
ing; to  the  south  of  this  has  also  been 
the  theatre  of  extensive  lava  displays. 
In  El  Dorado,  Calaveras,  and  other 
counties  are  other  table  mountains,  but 
in  Tuolumne  county,  one  hundred  and 
fifty  miles  south,  is  the  Table  Moun- 
tain which  has  become  so  celebrated  for 
its  connection  with  mining  operations 
and  the  discovery  of  fossil  remains.  Its 
mode  of  origin  is  not  different  from  the 
origin  of  those  in  Butte  county.  The 
summit  of  the  mountain  is  occupied  by 
a  heavy  bed  of  basaltic  lava  one  hun- 
dred and  forty  to  one  hundred  and  fifty 


r  W 


152 


GEOLOGICAL   STUDIES. 


feet  thick.  Its  width  is  about  1,700  feet.  Underneath  is  a  heavy 
deposit  of  detrital  material  very  distinctly  stratified  and  nearly 
horizontal,  composed  mostly  of  fine-grained  sandstone  or  feebly 
coherent  sand,  interstratified  in  which  are  fine  argillaceous  shales 
and  clays.  With  these  are  beds  of  gravelly  materials  strongly 
cohering  together,  and  called  "cement"  by  the  miners.  At  the 
bottom  is  the  "  pay  gravel  "  or  the  "  channel,"  a  body  of  coarse 
gravel  exactly  like  that  seen  in  the  bed  of  an  ordinary  river,  and 
here  gold-bearing.  The  entire  thickness  of  the  detrital  beds 
directly  under  the  centre  of  the  lava  is,  in  one  locality,  at  least 
fully  two  hundred  feet.  But  this  thickness  is  much  less  at  the 
edge  of  the  deposit,  owing  to  the  rise  of  the  underlying  vertical 
auriferous  slates  on  each  side,  as  shown  in  the  figure,  forming 
what  is  known  to  the  miners  everywhere  in  California  as  the 
"  rim  rock."  The  rim  rock  rises  here  fully  one  hundred  and 
fifty  feet  above  the  level  of  the  "pay  gravel."  The  latter,  occu- 
pying the  lowest  position,  is  four  or  five  feet  thick,  and  in  this 


FIG.  75.— TABLE  MOUNTAIN  IN  TUOLUMNE  COUNTY,  CAL.,  AT  THE  BUCKEYE  TUNNEL. 
£,  Lava  forming  the  table;  s,  Sandstone  under  the  lava;  <7,  Gravel;  si,  Slate;  j?,  Old 
river  bed;  R',  the  modern  river  bed;  T7,  Tunnel  through  the  "rim  slate"  to  the 
"deep  placers";  G^,  Modern  Gravel  and  "shallow  placers."  The  dotted  lines  indi- 
cate the  probable  configuration  of  the  surface  when  the  lava  was  erupted.  (Adapted 
from  Whitney.) 

place  is  eighty  feet  wide.  To  reach  this  gravel,  tunnels  are  run 
in  through  the  rim  rock,  as  shown  on  the  right,  or  sometimes 
through  the  cement.  When  the  channel  is  reached,  it  is  "  drift- 
ed" on,  the  miners  following  the  paying  streaks,  or  lines  of  aurif- 
erous gravel,  up  and  down  in  the  bed  of  the  ancient  water- 
course. 

What  else  but  a  water-course  could  this  trough  have  been  ? 
What  else  but  a  bed  of  river  gravel,  this  which  lies  strewn  along 


ANCIENT   LAVAS.  153 

the  bottom  of  the  channel  here  excavated  in  the  slates?  There 
was,  in  a  former  time,  a  stream  flowing  from  the  east  over  the 
outcropping  edges  of  the  auriferous  slates,  and  strewing  its  bed 
with  gravel  from  the  quartz  veins  in  the  slate.  On  each  side  was 
a  sufficient  rise  in  the  surface  to  bound  a  river  valley  as  indicated 
by  the  dotted  lines.  By  some  change  in  the  mode  of  action,  the 
sands  were  laid  down  over  the  gravel.  Then  came  an  enormous 
flow  of  lava  from  the  vents  of  the  Sierra,  occupying  the  entire 
bed  of  the  stream  and  partly  filling  the  valley.  The  stream  dis- 
placed wore  a  new  channel  along  the  border  of  the  lava  bed.  It 
wore  the  bounding  slope  away,  and  sunk  a  modern  channel  deeper 
than  the  old  one,  leaving  the  lava  to  cap  an  elevation  in  the  very 
place  where  once  was  the  valley.  The  modern  stream  brings 
auriferous  gravel  like  the  ancient  one.  These  are  the  "  shallow 
placers";  the  other  gravels  are  the  deep  placers. 

The  table  mountains  of  Butte  county  admit  of  a  similar 
explanation.  But  the  direction  of  the  modern  streams  in  this 
region  crosses  the  course  of  the  ancient  ones.  Many  impressive 


FIG.  76.— BASALTIC  PLATEAUX  OP  THE  COIRON,  ARDECHE.    (Scrope.) 

examples  of  a  similar  nature  occur  in  central  France,  some  of 
which  are  illustrated  in  Fig.  76. 

Many  remains  of  mammalian  quadrupeds  have  been  found  in 
the  deep  placers  of  California.  They  embrace  mastodon,  rhino- 
ceros, and  extinct  species  of  horse,  species  of  hippopotamus  and 
camel  related  to  the  living  species,  and,  finally,  several  human 


154  GEOLOGICAL   STUDIES. 

bones,  including  an  imperfect  skull.  The  question  remains  as  to 
the  precise  age  of  these  auriferous  gravels;  but  it  appears,  at 
least,  that  enormous  floods  of  lava  have  been  poured  out  over  the 
plains  and  valleys  of  the  western  slope  of  the  Sierra  since  man 
became  an  inhabitant  of  California. 

It  is  not  necessary  to  enter  further  into  particulars.  Not 
only  has  so  large  a  part  of  California  been  inundated  by  sheets 
of  molten  lava,  but  even  larger  areas  have  been  covered  in  other 
regions. of  our  Pacific  slope.  According  to  Leconte,  "the  great 
lava  flood  of  the  Northwest  covers  an  area  of  150,000  to  200,000 
square  miles,  and  is  3,000  to  4,000  feet  thick  in  its  thickest  part, 
where  cut  through  by  the  Columbia  River  at  the  *  cascades.'  r  In 
another  place,  at  least  seventy  miles  distant,  where  cut  into  2,500 
feet  deep  by  the  Des  Chutes  River,  at  least  thirty  successive 
sheets  may  be  counted.  Another  great  lava  flood,  according  to 
Gilbert,  covers  25,000  square  miles  of  Arizona,  and  is  3,000  feet 
thick  in  its  thickest  portions.  In  New  Mexico,  according  to 
Captain  Button,  the  San  Mateo  Mountains  are  a  volcanic  pile 
11,380  feet  high,  carved  into  numerous  spurs  by  magnificent 
gorges.  From  this  centre  the  lavas  reach  out  for  forty-five  miles 
to  the  north-north-east,  and  in  other  directions  for  eighteen  to 
thirty  miles.  The  lava  forms  a  superficial  sheet  over  each 
mesa  or  table,  ranging  in  thickness  from  fifty  to  two  hun- 
dred feet.  Many  of  the  vents  scattered  around  the  flanks  of 
Mt.  Taylor  can  be  easily  identified.  The  "  necks "  or  "  chim- 
neys" which  are  left  standing  in  the  valley  plains  beyond 
the  farthest  verge  of  the  lava-capped  mesas  are  among  the 
most  striking  features  of  the  country.  One  is  nearly  2,000  feet 
high. 

Those  who  have  visited  the  "  Giant's  Causeway  "  or  Fingal's 
Cave  have  seen  other  great  masses  of  rocky  material,  having  all 
the  essential  characters  of  lava  erupted  from  volcanoes.  These 
are,  indeed,  the  results  of  igneous  eruption,  though  there  be  no 
mountain,  and  no  discovered  point  where  the  outflow  took  place. 
It  escaped  through  fissures.  One  travelling  along  the  highway  in 
the  valley  of  the  Connecticut  south  of  Hartford  may  notice  at 


ANCIENT   LAVAS. 


155 


intervals  an  abrupt  ridge  running  in  a  straight  line  across  the 

alluvial  meadows.  Examina- 
tion discloses  the  existence  of  a 
vertical  wall  of  rock  rising  from 
the  underlying  sandstone  and 
rising  out  of  it.  The  nature 
of  the  rock  is  essentially  lava- 
like.  It  seems  to  have  been  lava 
which  rose  in  a  molten  state 
through  a  fissure  in  the  stratified  sandstones  beneath.  This  is  called 
a  dike.  Dikes  of  melaphyr  are  shown  in  Fig.  46,  and  an  actual 
group  of  trachytic  dikes  in  Fig.  83.  In  the  Meriden  Mountains, 
not  far  away,  we  discover  masses  of  ancient  lava  which  have 
risen  through  such  dikes.  The  outflows  continue  along  the  val- 


FIG.  77.— DIKES.  (See  also  Fig.  83.)  A  is 
harder  than  the  contiguous  strata,  and  B 
is  softer. 


FIG.  78.— BASALTIC  COLUMNS  ON  SEDIMENTARY  ROCK.    HAVING  THE  COOLING  SURFACE 
HORIZONTAL.    (After  Owen.) 

ley  of  the  Connecticut  to  New  Haven,  where  prominent  head- 
lands are  known  as  "  East  Rock  "  and  "  West  Rock."  Travelling 
up  the  Hudson,  our  attention  is  arrested  by  the  "  Palisades," 
which  are  only  another  mass  of  ancient  lava  erupted,  like  the 
Giant's  Causeway,  without  the  intervention  of  a  volcanic  moun- 
tain. In  Fig.  46  is  shown  a  basaltic  outflow,  intended  to  illus- 
trate basaltic  formations  in  various  parts  of  the  world.  Basaltic 


156 


GEOLOGICAL   STUDIES. 


outflows  often  assume  columnar  form,  and  we  observe  that  the 
axis  of  the  column  is  always  at  right  angles  with  the  cooling  sur- 
face. In  Fig.  78  the  columns  are  vertical  because  the  cooling 
surfaces  were  horizontal.  In  Fig.  79,  which  shows  a  dike  of 
basalt,  the  columns  are  horizontal  because  the  cooling  surfaces 
were  vertical.  If  we  take  a  mass  of  wet  starch  and  allow  it  to 


FIG.  79.— BASALTIC  PRISMS  FORMED  IN  A  DIKE.    HAVING  THE  COOLING  SURFACES  VERTI- 
CAL.   (After  Owen.) 

cool  rapidly,  a  similar  prismatic  structure  is  developed,  as  is  seen 
in  the  laundry  starch  of  the  markets.  The  form  is  perhaps  due 
to  general  shrinkage.  Possibly  ancient  lavas,  while  cooling, 
developed  a  similar  structure  from  the 
same  cause. 

At  Keweenaw  Point,  or  its  vicinity, 
on  the  south  shore  of  Lake  Superior, 
are  the  evidences  of  an  enormous  out- 
flow of  molten  lava,  which  issued  in 
very  remote  times,  and  spread  out 
in  numerous  sheets,  alternating  with 
sheets  of  pebbles,  which  have  become 
cemented  into  conglomerate.  In  this 
occurs  the  native  copper.  Much  of  this 
lava  presents  the  character  of  amygda- 
loid, Fig.  80.  When  cooling,  it  abound- 


FIG.  80.-ScoRiACEOus  LAVA,  IN 
PART  CONVERTED  INTO  AMYG- 
DALOID. CENTRAL  FRANCE. 

(Lyell.) 


ANCIENT   LAVAS. 


157 


ed  in  bubbles  of  gases,  and  became  exceedingly  vesicular,  like 
some  scoriae  of  modern  volcanoes.  After  the  gases  escaped,  the 
cavities  were  filled  with  various  minerals,  infiltrated  in  a  state  of 
solution.  The  rock  receives  its  name  from  the  almond-shaped 
inclusions,  and  it  retains  the  name  even  after  the  minerals  have 
dissolved  out. 

The  Geological  Survey  of  Italy  has  lately  published  sections 
of  the  island  of  Elba,  which  show  a  mass  of  Eocene  strata  inter- 


FIG.  81.— SECTION  ON  THE  WEST  PART  OF  THE  ISLAND  OP  ELBA,  900  METRES.    P,  Cape 
Poro;  E,  Bardella  Point;  /,  Limestone;  s,  Schists;  p,  Porphyry.    (Geol.  Surv.  Italy.) 

penetrated  and  interbedded  in  an  extraordinary  manner,  with 
dikes  and  intrusions  of  porphyry,  which  materially  swell  the  mass 
of  the  island.  Fig.  81  is  one  of  the  sections. 

Mr.  G.  K.  Gilbert,  in  a  report  on  the  Henry  Mountains,  of 
Utah,  has  made  us  acquainted  with  an  extreme  development  of 
intrusive  lavas;  that 
is,  igneous  rocks 
forced  into  the 
seams  separating 
sedimentary  strata 
(Fig.  82).  Such 
cases  have  long  been 
known,  and  Fig.  46 
shows  porphyry  so 
intruded.  But  i  n 
the  Henry  and  other  FlG-  8-— IDEAL  CROSS-SECTION  OP  A  "LAccoLiTE,"1  WITH 

*  ACCOMPANYING  SHEETS  AND  DIKES.     (Gilbert.) 

western    mountains, 

the  force  and  volume  of  the  intrusion  have  been  such  as  to  actu- 
ally lift  the  overlying  masses  of  strata,  as  here  illustrated.  Sub- 
sequently, erosions  have  in  some  cases  worn  away  the  overlying 
strata,  and  the  included  porphyritic  trachyte  is  gnawed  into 


158  GEOLOGICAL   STUDIES. 

many  fantastic  shapes.  The  crest  of  Mt.  Holmes  (Fig.  83)  affords 
an  excellent  illustration  of  dikes. 

Recurring  again  to  Fig.  46,  we  notice  a  representation  of  a 
vein  of  granite  injected  into  another  mass  of  granite.  It  is  the 
general  opinion  that  granite,  in  vein  form,  must  have  cooled 
from  igneous  fusion;  but  there  are  some  who  think  otherwise. 
You  see,  also,  that  rocks  of  the  eruptive  class  include  also  por- 
phyries and  other  varieties  somewhat  different  from  common 
lavas. 

The  observations  which  we  have  made  in  the  last  three  studies 
show: 

1.  That  the  internal  temperature  of  the  earth  increases  as 
we  penetrate  downward.  There  is  consequently,  and  necessarily, 
a  constant  transfer  of  heat  from  the  deeper  and  warmer  parts  to 


FIG.  83. — THE  CREST  OF  MT.  HOLMES,  UTAH.    (Gilbert.) 

the  shallower  and  cooler  parts.  In  other  words  there  is  a  contin- 
ual flow  of  heat  from  the  interior  to  the  surface,  and  a  final  radi- 
ation and  wastage  of  it  from  the  surface.  Thus  the  simple  fact 
of  internal  increase  of  heat  proves  that  the  earth  is  now  cooling. 
2.  The  numerous  evidences  of  more  highly  heated  conditions 
at  the  surface  in  ages  past  are  proof  that  the  cooling  process  has 
been  long  going  on.  Our  earth  must  therefore  be  contemplated 
as  a  cooling  body.  Many  of  the  most  important  events  in  its 
physical  history  are  known  to  have  resulted  as  incidents  of  cool- 
ing. The  fact  of  cooling  has  been  a  determinative  principle  in 


ANCIENT   LAVAS.  159 

terrestrial  progress.  It  has  had  something  to  do  with  the  earth's 
physical  vicissitudes  and  resultant  forms.  Through  these  it  has 
necessarily  exerted  conditioning  influences  on  the  organic  beings 
which  have  populated  its  surface. 

From  what  former  high  temperature  has  the  cooling  pro- 
ceeded ?  Most  of  those  who  speculate  on  this  question  agree  that 
the  whole  earth  was  once  in  a  state  of  igneous  fluidity.  Not  dis- 
covering any  reason  to  conclude  that  even  this  was  the  starting 
point  of  the  process  of  cooling,  they  carry  the  history  of  terres- 
trial matter  back  to  a  state  of  molten  mist  floating  in  a  gaseous 
medium. 

EXERCISES. 

What  is  the  evidence  of  the  tilting  of  the  cretaceous  strata  at  Tuscan 
Springs,  before  the  lava  was  poured  out?  What  is  the  proof  of  a  subsequent 
tilting?  Which  way  do  the  strata  dip  at  Tuscan  Springs?  Can  you  draw^, 
diagram  indicating  the  termination  of  the  Cretaceous  strata  at  a  higher 
level  than  at  the  springs?  What  is  the  evidence  of  the  existence  of  such 
higher  outcrop?  How  does  the  water  become  warmed?  How  does  it  obtain 
its  mineral  properties?  How  can  you  reconcile  the  northeasterly  dip  of  the 
auriferous  slates  with  the  fact  that  the  Sierra  lies  in  that  direction?  How 
can  the  Cretaceous  sandstones  over  them  be  nearly  horizontal?  Can  you  ex- 
plain why  they  dip  slightly  in  the  opposite  direction?  What  is  the  source  of 
the  "pay  gravel"  in  the  deep  placers?  By  what  streams  transported? 
What  is  the  difference  between  these  and  the  shallow  placers?  After  a  lava 
stream  displaced  the  old  river,  how  came  a  new  channel  into  existence  on 
each  side  of  the  lava  stream?  What  is  the  evidence  that  the  ancient  streams 
of  Butte  county  ran  across  the  direction  of  the  modern  streams?  Have  you 
ever  seen  a  deposit  of  volcanic  rock?  What  locality  of  volcanic  rocks  is 
nearest  to  this  place?  Could  vesicular  lavas  form  if  the  cooling  took  place 
under  great  pressure?  Why  do  you  answer  thus?  Do  you  think  the  tra- 
chyte of  the  Henry  Mountains  is  vesicular  or  compact?  Why  do  you  answer 
thus?  Are  amygdaloids  of  sedimentary  origin  or  not?  Are  they  metamor- 
phic  ?  Do  they  denote  any  particular  kind  of  eruptive  rock?  Does  the  des- 
ignation relate  to  composition  or  to  structure? 


160  GEOLOGICAL   STUDIES. 


STUDY  XXV.— Mountain  Phenomena. 

Let  us  trace  somewhat  farther  the  results  of  disturbances  of 
the  earth's  crust.  If  we  turn  back  to  Fig.  38,  we  notice  that  the 
disturbance  of  the  strata  results  in  an  elevation  of  surface  having 
the  appearance  of  a  mountain.  You  have  already  recognized 
here  the  indications  of  an  upheaval  of  the  granite  mass  which 
seems  to  burst  through  the  beds  of  gneiss  once  overlying.  This 
figure  may  be  taken  as  a  general  section  across  the  Laurentian 
mountains  of  Canada  or  the  Adirondacks  of  New  York.  The 
Humboldt,  Wahsatch  and  many  other  mountains  exhibit  a  simi- 
lar structure.  But  we  are  not  certain  the  central  mass  becomes 
exposed  to  view  in  consequence  of  protruding  through  the  over- 
lying rocks.  Perhaps  the  gneisses  or  other  strata  continued  to 
ctmceal  the  granite  or  other  central  core,  after  the  upheaval,  and 
have  been  subsequently  worn  away.  It  is  also  quite  supposable 
that  a  granite  summit  was  originally  uplifted  above  the  sea 
level,  and  the  gneisses  when  forming  as  sediments  never  covered 
that  portion  of  the  granite  now  exposed  to  view.  It  requires 
sometimes  much  study  to  determine  in  which  way  it  happened  that 
the  central  mass,  whether  granitic  or  not,  stands  uncovered  by 
later  strata.  In  the  case  of  the  Laurentian  mountains  and  the 
Adirondacks,  the  third  explanation  is  held  to  be  the  true  one. 

The  section  through  Tennessee,  Fig.  33,  which  we  have  used 
to  illustrate  erosion,  is  also  a  good  illustration  of  two  kinds  of 
mountain  structure.  At  the  east  we  see  the  massive  strata  of 
the  Unaka  ranges  standing  at  a  very  high  inclination,  and  rising 
to  an  average  altitude  of  5,000  feet,  along  the  entire  eastern  bor- 
der of  the  state.  We  find  at  least  twenty-two  summits  which 
exceed  6,-000  feet  in  altitude.  These  rocks,  according  to  Safford, 
are  chiefly  thick  beds  of  sandstones  and  conglomerates  of  the 
Primordial  Group  (see  Fig.  39),  partly  in  a  metamorphic  state  — 
that  is,  changed  to  gneisses  and  schists.  There  are  two,  and  for 
part  of  the  distance,  three  parallel  ranges  constituting  the  Unaka 
chain,  and  this  is  a  part  of  the  great  Appalachian  chain,  stretch- 


MOUNTAIN    PHENOMENA. 


161 


ing  from  New  England  to  central  Alabama.  The  strata  of  the 
Unaka  ranges  are  seen  to  be  monoclinal  —  having  the  dips  all  in 
the  same  direction.  This  may  be  distinguished  from  the  anti- 
clinal structure. 

Recurring  again  to  the  section  through  Tennessee,  we  observe 
a  fine  example  of  another  class  of  mountains.  The  Cumberland 
table  land  stands  at  a  mean  elevation  of  2,000  feet  above  sea 
level.  It  is  a  flat-topped  mountain  from  fifty  to  seventy-five  miles 
in  width,  and  stretching  from  Georgia  through  Tennessee  and 
Kentucky.  It  can  indeed  be  traced  through  West  Virginia  and 


FIG.  84. —  SECTION  FROM  THE  CATSKILL  MOUNTAINS  TO  THE  HUDSON  RIVER.    (Mather.) 

Pennsylvania  into  southern  New  York.  It  subsides  in  northeast- 
ern Alabama.  As  we  inspect  this  east  and  west  section  through 
the  table  land,  it  becomes  obvious  that  this  is  not  a  mountain 
mass  which  has  been  upheaved,  but  is  a  region  of  relief,  result- 
ing from  vast  erosions  along  its  eastern  and  western  sides.  The 
contiguous  valleys  have  been  excavated.  The  strata,  moreover, 
remain  nearly  horizontal.  They  have  not  been  disturbed.  They 
consist  of  rocks  of  Upper  Carboniferous  age.  Lookout  Moun- 
tain and  Missionary  Ridge,  the  sites  of  important  battles,  are 
outliers  of  this  great  table  land.  Mountains  of  relief  are  styled 
by  Powell,  "cameo  mountains." 

The  Catskill  Mountains  present  a  similar  structure  (Fig.  84), 
consisting  of  nearly  horizontal  beds,  but  having  a  slight  dip  south- 
west, piled  up  two,  three,  or  four  thousand  feet  above  sea  level. 
They  belong  to  the  age  of  the  Devonian.  The  Uinta  Mountains 
are  somewhat  in  the  form  of  a  table  land;  but  they  are  not  a 


162 


GEOLOGICAL   STUDIES. 


proper  table  land,  since  upheaval  as  well  as  erosion  has  been  con- 
cerned in  the  production  of  the  salience.  They  are  one  hundred 
and  fifty  miles  long  and  fifty  broad.  In  Fig.  85  is  presented  an 
idealized  section,  from  Powell,  showing  a  mass  of  folded  strata 
in  the  interior,  over  which  passes  a  broad  swell,  which  has  been 
extensively  eroded  and  flattened  along  the  top.  Actual  observa- 
tion has  not  extended  below  the  level  of  A  B.  C  D  is  the  sea 
level,  and  Y  is  the  bed  of  the  Green  River,  which  has  been  ena- 
bled to  cut  through  the  mountain,  because  it  existed  before  the 
mountain,  and  the  mountain  slowly  rose  under  it,  as  a  log  moves 
on  a  saw.  The  river,  then,  as  Powell  suggests,  has  sawed  the 
mountain  in  two.  The  actual  elevation  of  this  fold  was  about 


,>-- 


GENERALIZED  SECTION  THROUGH  THE  UINTA  MOUNTAINS,  FROM  NORTH  TO 
SOUTH.    (Powell.) 

30,000  feet.  The  mean  depth  of  the  degradation  from  the  sum- 
mit is  three  and  a  half  miles,  and  as  the  area  of  the  mountain 
proper  is  about  2,000  square  miles,  the  total  degradation  is  7,000 
cubic  miles.  The  materials  were  deposited  in  the  bottom  of  the 
ocean  then  contiguous.  This  took  place  during  the  earlier  Eocene. 
On  the  north  the  sedimentation  partly  supplied  from  this  source 
amounted  to  more  than  6,000  feet,  and  in  some  parts  to  8,000 
feet.  We  thus  get  new  illustrations  of  doctrines  previously 
generalized. 

From  what  we  have  already  seen,  it  is  apparent  that  different 
portions  of  the  earth's  crust  have  been  subject  to  considerable 


MOUNTAIN    PHENOMENA.  163 

vertical  movements.  These  could  hardly  be  conceived  to  take 
place  without  extensive  fracturing  of  the  strata.  In  fact,  a  re- 
examination  of  some  of  our  sections,  which  are  simply  pictures 
from  nature,  will  disclose  the  presence  of  fractures.  In  the  sec- 
tion through  Tennessee  (Fig.  33)  we  find  a  break  some  distance 
east  of  the  Cumberland  table  land.  Notice  that  the  strata  on 
opposite  sides  dip  in  opposite  directions,  and  do  not  correspond 
together.  On  the  eastern  border  of  the  valley  of  East  Tennes- 
see is  another  break,  and  the  strata  on  opposite  sides  have  differ- 
ent inclinations,  and  do  not  correspond.  Such  an  occurrence  is 
called  a  fault ,  or  dislocation.  Many  times  the  rocks  on  one  side 
of  the  fault  have  been  raised  or  lowered  more  or  less  from  their 
original  position,  and  sometimes  considerable  movements  have 

WASATCH  PLATEAU 
Faults  from  600  to  l,700/ee<  11.000/f.  high 

,  XT •  'i  rnTTr-T-r--!-. —      E 


c  b          c          c         b  a 

FIG.  86. — SECTION  EAST  AND  WEST  IN  CENTRAL  UTAH,  SHOWING  NUMEROUS  FAULTS. 
a,  Triassic;  &,  Jurassic;  c,  Cretaceous;  c?,  Laramie;  £/,  Tertiary.     (Button.) 

taken  place.  Vast  dislocations  'exist  elsewhere  in  the  Appalach- 
ians, and  this  is  indicated  in  the  diagram,  Fig.  34.  In  several 
cases  the  downthrow  amounts  to  5,000  or  10,000  feet;  and  Lesley 
gives  an  account  of  a  fault  not  less  than  20,000  feet,  bringing 
upper  Devonian  strata  on  one  side  opposite  the  lowest  Cambrian 
on  the  other. 

Some  of  the  grandest  fractures  and  faultings  known  in  the 
world  occur  in  the  Rocky  Mountains  and  the  regions  farther 
west.  The  anticlinal  of  the  Park  Range  of  the  Rocky  Mountains 
was  cleft  down  the  axis,  and  the  eastern  half  depressed  10,000 
feet.  Colorado  Range  was  severed  by  an  enormous  southeast- 
northwest  fault,  which  dropped  the  region  of  the  Laramie  Hills 
6,000  or  7,000  feet  lower  than  the  southern  continuation  of  the 
same  ridge.  The  inclined  easterly  dipping  Palaeozoic  and  Meso- 


Paria  Plateau, 


Virgen  Valley. 
Pine  Valley  Mountain. 


Paria  Fold. 
Echo  Cliffs. 


Marble  Canon. 

East  Kaibab  Fold. 

Kaibab  Plateau. 
West  Kaibab  Fold, 
Kanab  Plateau. 
Kanab  Canon. 

Kanab  Plateau. 

To-ro"-weap  Fault. 
U-in-kar-et  Mountains. 

Hurricane  Fault. 
Shi-vwits  Plateau. 


Grand  Wash  Fault 
Grand  Wash. 


MOUNTAIN    PHENOMENA. 


165 


zoic  rocks  of  the  Wahsatch,  in  the  region  of  the  Cottonwood, 
rested  against  the  abrupt,  precipitous  face  of  a  granite  cliff,  of 
which  30,000  feet  are  now  exposed  (King).  In  Fig.  86  we  have 
a  section  in  central  Utah,  showing  seven  faults.  The  great  fold 
of  the  Uinta  Mountains  produces,  along  some  parts  of  its  bor- 
ders, so  sharp  a  flexure  that  the  strata  are  broken  and  faulted. 
A  great  fracture  runs  along  the  axis  of  the  Sierra  Nevada  for 
300  miles,  accompanied  by  a  dislocation  of  3,000  to  10,000  feet. 
For  a  large  part  of  this  distance  the  eastern  half  of  the  split  fold 
has  sunken  down  to  a  level  with  the  plain,  while  the  western  half 
remains  elevated.  The  consequence  is,  that  the  mountain  pre- 
sents a  gentle  slope  on  the  west,  and  a  very  precipitous  one  on 
the  east.  This  appears,  consequently,  to  be  a  mountain  of  a  type 
different  from  any  before  distinctly  mentioned.  It  is  a  mono- 


FIG.  88.— GKAYLOCK,  A  SYNCLINAL  MOUNTAIN.  (Emmons.)  £,  Graylock;  ff,  Hoosac 
Mountain  and  Tunnel;  A,  North  Adams;  I,  I,  "Eolian  Limestone  "  (Trenton);  t,  Tal- 
coid  Schist;  m,  Mica  Schist;  ^,  Gneiss;  «,  Steatite. 

clinal  mountain,  but  the  continuity  of  the  strata  is  not  inter- 
rupted by  erosion,  but  by  precipitation  into  the  abyss.  Similarly 
the  Wahsatch  range  has  been  cleft  by  a  fault  at  least  100  miles 
long,  and  the  west  half  has  sunken  40,000  feet  (King).  As  the 
faulting  process  has  had  so  much  to  do  with  the  surface  config- 
uration of  the  plateau  region  of  the  West,  we  reproduce  in  Fig. 
87,  from  Powell,  a  bird's-eye  view  of  the  great  Colorado  plateau 
north  of  the  Grand  Caiion  shown  in  the  sketch,  Fig.  31.  This  will 
be  convenient  for  reference  in  connection  with  other  points  of  geo- 
logical interest. 

In  Fig.  88  is  shown  another  variety  of  mountain.  This  is  a 
synclinal  mountain,  or  one  in  which  the  dips  of  the  strata  are 
from  opposite  sides  toward  the  centre  of  the  mountain.  Corre- 
spondingly, the  contiguous  valleys  are  anticlinal.  This  results 


166 


GEOLOGICAL    STUDIES. 


from  the  more  rapid  erosion  experienced  along  the  exposed  and, 
probably,  fractured  anticlinal  crest.  In  consequence,  the  actual 
original  crest  has  been  lowered  below  the  level  of  the  valley,  and 


FIG.  89. — SECTION  THROUGH  MT.  KEAKSAKGE,  N.  H.,  SHOWING  SYNCLINAL  STRUCTURE. 
(C.  H.  Hitchcock.)     W,  Wilmot;  W  H,  Wilmot  House;   Wh  H,  White  House;  P, 
Plumbago  Pt. ;  a,  Porphyritic  Gneiss;  &,  Andalusite  Mica  Schist;  c,  Granite. 

the  valley  stands  forth  as  an  elevation.     Thus  a  valley  comes  into 
existence  where  the  mountain  was,  and  a  mountain  remains  where 


FIG.  90.— THE  NEEDLES  OF  CHARMOZ  AND  THE  MER  DE  GLACE,  SWITZERLAND. 
(Photograph.) 

the  valley  was.  Mt.  Kearsarge,  in  New  Hampshire  (Fig.  89),  is 
one  of  many  illustrations.  It  is  one  of  the  various  results  of  the 
combined  action  of  upheaval  and  erosion. 


MOUNTAIN"    PHENOMENA. 


16? 


In  Figs.  90  and  91  we  have  views  of  a  type  of  mountains 
resulting  from  a  vertical  position  of  schistose  rocks  sharpened  by 
weathering.  These  are  the  well  known  "  needles  "  (aiguilles]  of 
the  Alpine  ranges. 

Now  let  us  reduce  to  a  systematic  statement  the  various  types 
of  mountain  structure  to  which  our  attention  has  been  directed, 
whether  in  this  study  or  preceding  ones. 


FIG.  91.— CASTLE  ROCK  RANGE,  CAL.     (Whitney.) 


TYPES  OF  MOUNTAIN  STRUCTURE. 

I.    Sedimentary.     The  mountain  mass  composed  of  sedimentary  rocks. 
1.    UPHEAVAL,  modified  by  subsequent  denudation. 
(1)  Anticlinal  in  origin  and  fundamental  form. 

(a)  Amphiclinal  in  actual  form.     Actual  dips  both  ways. 

Rocky  Mountain  and  Basin  Ranges, 
(a)  Central  mass  an  antecedent  exposure — primordial. 

Laurentian,  Adirondac,  Humboldt. 
(/9)  Central  mass  protruded,  or  revealed  by  denudation. 

Mill  Mountain,  Va.,  Pifion  and  Diamond  ranges. 
(5)  Monoclinal  in  actual  form, 
(a)  Resulting  from  denudation. 

Unaka  Mountains,  Tenn.  and  N.  C. ;  Wolf  Ridge,  Va. 
(,3)  Resulting  from  faulting. 
Elk  Mountains,  Sierra  Nevada,  Wahsatch,  many  Basin  ranges. 

Typical  structure  of  Rocky  Mountains.     (Button.) 
(c)  Orthoclinal,   with    the  strata  vertical   (generally    sharpened    by 

erosion). 
Afpine  "Needles."     Castle  Rock  range,  Cal. 


168  GEOLOGICAL   STUDIES. 

(d)  Hyperclinal,  or  "Fan  Structure."     Tilting  carried  beyond   the 

vertical. 

Mont  Blanc,  St.  Gothard,  San  Luis,  and  Santa  Lucia,  Cal. 
(2)  Aclinal.     Strata  horizontal  or  nearly  so. 
(a)  Bounded  by  monoclinals.     Uinta  mountains. 

(5)  Bounded  by  faults.     Kaibab  structure  of  Powell.     (Runs  into  pre- 
ceding.) 

Common  in  the  "Plateau  Province." 
2.    RELIEF.     Salience  resulting  from  contiguous  erosions. 

(1)  Tabular.     Stratification  horizontal. 

Cumberland  Mountains,  Catskills,  House  Mountain,  Ya. 

(2)  Synclinal.     Strata  dipping  into  the  mountain  from  opposite  sides. 

Mt.  Kearsarge,  K  H. ;  Becraft's  Mountain,  N.  Y. ;  Mt,  Eolus, 
Yt.,  Graylock,  Mass.,  Mt.  Everett,  Mass. 

II.  Eruptive. 

1.  Material  a  deposition.     Ejected,  and  brought  down  by  gravity. 

(1)  Yolcanic  cones  of  ashes  and  cinders  (generally  with  lava  added). 

JEtna,  Yesuvius,  Shasta,  Mauna  Loa. 

(2)  Yolcanic  sheets  of    ashes  and  cinders,    subsequently  eroded    into 

saliences.     Erupted  depositions  of  Oregon.     Peperino  beds  of 
Italy  and  elsewhere. 

2.  Outflow  of  molten  matter  forming  sheets,  subsequently  eroded. 

Lava  mesas  and  mountains.     Ridges  near  Silver  City,  Col. 

III.  Combined.     Strata  uplifted  by  intrusions  beneath. 

1.  Turgescence  of  crust.     Action  producing  fractures  and  an  excess  of 

dykes  and  veins.     Island  of  Elba. 

2.  Laccolites.     Action  intrusive.     Laccolites  variously  eroded. 

Henry  Mountains,    Sierra   Abajo,    El   Late,    Navajo  Mountain, 
Indian  Creek,  Wy. 

EXERCISES. 

When  we  find  a  region  having  granitic  rocks  at  the  surface,  why  are 
there  no  other  rocks  over  the  granite?  Can  you  be  certain  of  the  reason  why 
the  granite  is  exposed?  Suppose  the  granite  is  much  higher  than  the  nearest 
newer  rocks,  what  then  would  you  conclude?  What,  if  the  granite  exposure 
is  lower  than  neighboring  rocks  of  later  date?  How  do  you  know  when 
rocks  are  of  later  date  than  the  granite?  Suppose  we  find  a  mountain  with- 
out granite  exposed  at  the  summit,  does  it  probably  contain  granite?  In  the 
section  through  Tennessee,  Fig.  33,  point  out  two  types  of  mountain  struc- 
ture. In  what  direction  do  the  rocks  dip  in  the  Uriaka  mountains?  Is  this 
a  case  of  upheaval?  Is  this  an  anticlinal?  How  many  branches  or  sides  has 
an  anticlinal?  How  many  are  seen  in  the  Unakas?  Which  branch  is  present? 


MOUNTAIN    FORMATION.  169 

Where  is  the  other?  What  other  type  of  mountain  in  the  Tennessee  sec- 
tion? Is  this  also  a  case  of  upheaval?  Is  the  Uinta  Mountain  strictly  a  table 
land?  Has  there  been  any  upheaval  there?  How  does  this  case  differ  from 
an  ordinary  anticlinal?  How  do  we  know  that  the  Green  River,  which  has 
cut  through  it,  is  older  than  the  mountain  ?  If  the  river  flowing  south  had 
been  obstructed  by  the  mountain,  where  would  the  river  have  gone?  Would 
it  have  been  possible  for  other  streams  to  cut  the  mountain  in  other  direc- 
tions? What  is  the  extreme  extent  to  which  you  could  conceive  the  moun- 
tain cut  up?  How  might  a  detached  outlier  or  column  have  originated? 
How  do  we  know  the  formations  north  of  the  Uinta  were  derived  partly  from 
the  destruction  of  the  Uinta?  When  several  thousand  feet  of  sediments 
accumulate  on  a  sea  bottom,  do  you  think  the  bottom  would  tend  to  sink? 
Suppose  some  thousands  of  feet  are  removed  from  the  Uinta  mountains,  do 
you  think  the  unloading  would  cause  the  region  to  rise?  Look  at  Fig.  87 
and  point  out  the  faults.  Show  where  there  has  been  a  downthrow.  Show  a 
structure  somewhat  similar  to  that  of  the  Uinta  Mountains.  Point  out  val- 
leys of  erosion.  Do  the  Uinkaret  Mountains  look  like  anticlinals?  Does  the 
Pine  Valley  Mountain?  Where  is  the  Grand  Canon  in  this  view?  Which 
way  does  it  run?  In  what  direction  do  these  great  faults  run?  Draw  a  dia- 
gram to  explain  how  a  synclinal  mountain  might  originate. 


STUDY   XXVI.—  Mountain  Formation. 

We  now  present,  in  Fig.  92,  a  remarkable  section  in  the  Appa- 
lachian region,  worked  out  by  Prof.  J.  L.  Campbell.  All  the 
principal  varieties  of  mountain  structure  are  here  shown.  The 
strata  are  Cambrian,  Silurian  and  Devonian,  and  the  particular 
formations  are  indicated  by  numbers  and  letters  corresponding 
with  the  general  table  of  formations,  Pt.  II,  ch.  ii,  §5.  For  the 
purpose  of  showing  the  relation  of  the  different  kinds  of  rocks  to 
the  work  of  erosion,  the  conglomerates  are  distinguished  by  coarse 
dots,  sandstones  by  finer  ones,  shales  by  closely  ruled  lines,  while 
limestones  are  blocked,  and  those  of  different  periods  otherwise 
distinguished.  Here  will  be  noticed  two  great  faults.  The  mass 
between  them,  some  four  miles  long,  has  been  thrown  down. 
The  dotted  lines  indicate  the  former  extension  of  strata.  This 
section  must  be  much  studied.  It  is  substantially  a  real  section. 
Such  bendings,  altitudes  and  fractures  are  facts  scientifically 
worked  out. 


10  a.b. 


NVlill 

Mil. 


MOUNTAIN   FORMATION.  171 

A  free  glance  at  the  foregoing  section  conveys  the  distinct 
impression  that  a  pile  of  rocky  sheets  has  been  subjected  to  a 
folding  process,  and  afterward  extensively  denuded.  The  fold- 
ing process  has  in  some  places  fractured  the  strata,  and  caused 
dislocations.  It  is  quite  possible  that  the  faulting  was  a  subse- 
quent event.  If  this  section  were  again  flattened  out,  it  would 
increase  considerably  in  length.  In  the  process  of  folding, 
therefore,  the  original  length  must  have  diminished.  If  this  dia- 
gram were  exact,  and  made  to  measure,  we  might  lay  a  thread 
along  one  of  the  formations  from  end  to  end,  and  then  measure 
the  length  of  thread  required,  and  thus  ascertain  the  percentage 
of  shortening  in  consequence  of  the  folding.  King  estimated 
that  ten  per  cent  would  not  more  than  express  the  shortening  of 
the  strata  folded  up  along  the  belt  of  the  fortieth  parallel.  Some 
of  the  basin  ranges  have  even  undergone  a  longitudinal  shrink- 
age of  over  ten  per  cent.  (King,  S.  F.  Emmons.)  Claypole 
measured  a  section  sixty-five  miles  long,  across  Huntington, 
Juniata  and  Perry  counties,  in  Pennsylvania,  and  calculated  the 
original  length  of  the  strata  had  been  about  one  hundred  miles, 
giving  a  shrinkage  of  thirty-five  per  cent.  We  may  admit  that 
this  is  perhaps  an  exaggerated  estimate,  and  still  feel  certain 
that  enormous  shrinkage  of  a  folded  crust  must  take  place. 

A  little  reflection  makes  it  apparent,  also,  that  the  movement 
of  contraction  and  folding  must  be  the  result  of  pressure  from 
without.  A  linear  shortening,  accompanied  by  folding,  results 
from  pressure  from  the  ends.  There  must  have  been  some  enor- 
mous lateral  pressure  experienced  by  all  parts  of  the  folded 
crust.  This  conviction  is  strengthened  by  the  appearance  of 
the  heavy-topped  folds  which  resulted  in  the  upheaval  of  the 
Alps  of  central  Europe.  The  well  known  fan  structure  of  the 
Alps  is  a  remnant  of  the  huge  inflated  folds,  whose  extremities 
appear  to  have  been  pressed  together  by  the  continuance  of 
the  pressure  after  the  folds  had  been  formed.  (See  Fig.  93.) 

We  generalize,  therefore,  the  important  principle  of  lat- 
eral pressure  exerted  in  the  earttts  crust. 

Given  an  enormous  lateral  pressure,  then  either  the  contig- 


172 


GEOLOGICAL   STUDIES. 


uous  parts  of  the  crust  will  be 
crushed     together     and     inter- 
mingled, or  the  crust  will  break 
and  certain  strata  will  slide  over 
and  between  others;  or,  finally, 
the  crust  will  suffer  wrinkling, 
as    shown  in   Fig.    94.     When 
once  a  form  like  this  has  been 
inaugurated,  then,  evidently,  all 
increased  pressure  from  the  di- 
rections   A   and    B    will  tend 
further  to   elevate    a   and    de- 
press b  and  c.     When,  at  length, 
the  weight   of  the   fold    a  be- 
comes    very     great,     pressure 
from  the  directions  A  and  J?, 
instead  of  lifting  thefold higher, 
will    develop    new   folds  at    H 
and  6r.     The  new  folds  will  not 
arise  until  the  weight  of  a  be- 
comes sufficient  to  overcome  the 
rigidity  of  the  crust  at  .ZTand  6r. 
That  is,  when  the  crust  is  more 
rigid,   the   fold   a   will  be  sus- 
tained at  a  higher  altitude.      So 
we    deduce    the  principle   that 
the  highest  mountains  will  come 
into  existence  in  the  epoch  when 
the  crust  possesses  most  rigid- 
ity •  that  is,  in  times  geologi- 
cally recent;  because,  through 
terrestrial  cooling  and  contin- 
ued sedimentation,  the  crust  is 
becoming     thicker     and    more 
rigid.      A  study  of  mountains 
confirms  the  deduction,  since  all 


MOUNTAIN    FORMATION. 


173 


the  highest  mountains  are  composed  chiefly  of  Csenozoic  and  Meso- 
zoic  strata. 

To  illustrate  further  the  effects  of  lateral  pressure,  and  to  de- 
monstrate experimentally  a  probable  origin  of  many  mountains, 
M.  Favre,  of  Geneva,  devised  the  experiment  set  forth  in  Fig.  95. 
He  spread  a  layer  of  clay  on  a  stretched  sheet  of  India  rubber, 
and  allowed  the  sheet  slowly  to  contract.  The  sheet  may  be  five- 
eighths  of  an  inch  thick,  six  and  three-fourths  inches  wide,  and 
sixteen  inches  long.  When  stretched  to  twenty-four  inches,  it 
may  be  covered  with  a  layer  of  potters'  clay  from  one  to  three 
inches  thick,  made  as  adherent  as  possible  to  the  India  rub- 
ber, with  a  block  of  wood  applied  at  each  end.  The  slow 
contraction  of  the  Irfclia  rubber  develops  the  appearances  seen 


FIG.  94.— FORMATION  OF  WRINKLES  IN  THE  EARTH'S  CRUST,  WITH  PARALLEL  CONTIGUOUS 

FURROWS. 

in  the  figure.  Now,  when  you  carefully  inspect  this  figure, 
you  note  several  important  points  of  resemblance  to  the  moun- 
tain corrugations  on  the  earth's  surface  :  (1)  There  is  a  set 
of  folds  or  anticlinals.  (2)  Some  of  the  anticlinals  are  frac- 
tured along  the  crest.  (3)  The  folds  present  a  tendency  to  be 
elongated  in  a  direction  at  right  angles  to  the  direction  of 
the  pressure.  We  note,  also,  other  points  :  (1)  The  upper 
layers  are  more  folded  than  the  lower;  the  lower,  therefore, 
must  have  been  shortened  by  squeezing  together.  Perhaps  the 
lower  strata  in  the  earth's  crust  have  been  similarly  squeezed 
together,  or,  instead,  have  suffered  an  infinite  number  of  small 
plications  in  place  of  large  folds.  (2)  The  corrugations  are  scat- 
tered over  the  entire  surface,  instead  of  being  grouped  "like 


174 


GEOLOGICAL   STUDIES. 


mountain  ranges,  in  a  great  chain.  (3)  The  longitudinality  and 

parallelism  of  the  folds  arise  from  the 
fact  that  the  pressure  was  exerted  from 
two  directions.  As  mountains  present 
similar  characters,  we  may  infer  that 
they  also  receive  pressure  from  two 
opposite  directions.  These  seem  to  be 
facts  and  valid  inferences  as  far  as  they 
go. 

In  the  results  of  mountain  making 
we  seem  therefore  to  detect  the  evi- 
dences of  enormous  lateral  pressure  ex- 
erted from  all  directions,  but  especially 
from  directions  at  right  angles  with  the 
axes  of  mountain  ranges.  What  data 
have  we  for  inferring  the  origin  of  these 
pressures  ? 

Now,  our  attention  has  been  di- 
rected to  some  facts  which  seem  to 
indicate  that  the  earth  is  a  cooling 
body,  and  has  for  many  ages  been 
cooling.  A  cooling  process  is  a  shrink- 
ing process.  Hence  the  earth  has 
contracted  in  volume;  its  circumfer- 
ence has  become  less.  Now,  if  the  mat- 
ter of  the  crust  or  exterior  had  cooled 
at  the  same  rate  as  the  interior,  the 
shrunken  crust  would  still  fit  the 
shrunken  interior,  and  so  no  wrinkling 
would  be  possible.  But  the  crust  is  in 
a  position  between  the  heated  interior 
and  cold  external  space,  and  these  con- 
tending influences  hold  the  temperature 
of  the  crust  at  a  point  somewhat  uni- 
form; while  all  the  heat  emitted  by  the 
interior,  in  this  contest,  tends  continu- 


MOUNTAIN    FORMATION.  175 

ally  to  reduce  its  temperature.  While  therefore,  the  interior 
shrinks,  the  crust  retains  its  ancient  circumference.  It  is  there- 
fore obliged  to  wrinkle  to  dispose  of  the  surplusage. 

But  a  general  shrinkage  of  the  earth  would  thus  result  in 
a  process  of  crustal  wrinkling  having  no  relations  to  parallels  or 
meridians.  It  would  be  a  wrinkling  like  that  of  the  skin  of  a 
withered  apple.  There  must  be,  to  produce  our  meridionally  dis- 
posed mountains,  some  force  acting  more  energetically  from  east 
to  west  than  from  north  to  south;  or  else  there  must  exist  in  the 
crust  some  ingrained  predisposition  to  yield  to  the  action  of  east 
and  west  forces. 

Now,  I  think  it  may  be  shown  that  both  causes  have  existed, 
but  the  exposition  of  them  would  carry  the  elementary  student 
too  far.  Let  us  therefore  simply  state  the  principles  and  await 
the  opportunity  for  their  full  comprehension.  (1)  The  earth  has 
shrunken  more  along  its  east  and  icest  circumference  than  along 
its  north  and  south  circumference.  This  has  resulted  from  dimin- 
ishing oblateness  due  to  gradually  retarded  rotation.  (2)  In- 
grained meridional  predispositions  exist.  I  have  elsewhere  sug- 
gested that  the  tidal  action  of  the  moon  while  the  earth  was  yet 
in  the  incrustive  stage,  must  have  implanted  a  meridional  struc- 
ture which  predisposed  to  wrinkling  more  considerably  in  the 
north-south  direction  than  in  the  east^west  direction.  Ocean 
pressures  could  have  had  no  agency  in  initiating  the  direction  of 
mountain  trends,  since  the  axes  of  the  earth's  folds  existed  before 
the  oceans,  and  the  bounds  of  the  oceans  were  indeed  determined 
bv  them  from  the  beginning. 

If  we  glance  again  at  the  plateaus  of  the  Grand  Canon  (Fig. 
87),  we  see  a  vast  region  shivered  by  faults.  We  see  great  slabs 
of  the  earth's  crust  uplifted  on  one  or  more  sides,  sometimes  to 
mountain  altitudes.  Now  while  some  fracturing  of  the  crust 
must  have  accompanied  the  actions  which  upraised  mountain  folds, 
we  cannot  conceive  of  huge  unbent  slabs  as  a  product  of  action 
whose  characteristic  it  is  to  produce  bent  and  crumpled  rocky 
sheets.  Here  we  have  the  evidences  of  a  force  acting  vertically, 
not  tangentially.  It  is  as  if  an  ice-covered  lake  had  been  par- 


176  GEOLOGICAL    STUDIES. 

tially  drained.  The  ice  subsides  and  undergoes  fracture  along 
countless  sub-parallel  and  intersecting  lines.  Should  the  lake  be 
again  filled,  arid  then  again  drained,  and  this  process  several 
times  repeated,  the  joints  in  the  ice  would  be  opened;  there 
would  arise  dislocations.  Some  cuboidal  masses  would  be  lifted 
up.  The  accompanying  lateral  motion  would  throw  some  into 
confusion,  and  the  whole  would  present  some  resemblance  to  the 
actual  aspect  of  these  plateaus.  Now  we  have  the  evidence  of 
a  most  copious  escape  of  molten  matter  from  beneath  the  crust 
of  the  plateaus  during  the  later  stages  of  the  continent's  history. 
In  the  present  state  of  our  knoweldge,  perhaps  we  can  do  no  bet- 
ter than  to  connect  with  these  lava  outflows  such  fluctuations  in 
the  level  of  the  crust  as  might  explain  the  great  system  of  fault- 
ings  so  characteristic  of  western  geology. 

Thus,  our  attention  has  been  directed  to  the  most  obvious 
characteristics  of  mountain  forms  and  mountain  mechanism;  and 
we  have  tried  to  infer  from  the  phenomena,  the  way  in  which  the 
known  forces  must  or  may  have  acted  to  produce  them.  The 
methods  of  mountain  making  are  not  yet  fully  understood;  but 
as  far  as  we  have  here  gone,  our  inferences  probably  represent 
the  truth.  The  whole  subject  is  too  large  and  too  difficult -for  the 
elementary  student,  and  he  should  return  to  it  in  an  advanced 
course. 

EXERCISES. 

Look  at  Fig.  92  and  point  out  the  easterly  end  of  the  section.  Draw  a 
line  on  the  map  showing  where  this  section  is  located.  What  mountains 
does  it  cross?  Why  is  it  not  drawn  exactly  east  and  west  ?  What  is  the  high- 
est peak?  What  is  its  height?  What  is  the  lowest  point  and  its  elevation? 
If  you  were  on  the  summit  of  the  highest  mountain,  what  would  be  the  age 
of  the  rocks  under  your  feet?  Look,  at  the  Table  of  Types  of  Mountain 
Structures  and  point  out  the  type  to  which  this  belongs.  Point  out  others 
of  the  same  type.  How  much  do  you  estimate  the  highest  mountain  to  have 
been  lowered?  By  what  means  was  it  lowered?  What  type  is  Furnace 
Mountain?  What  type  is  the  Hog  Back?  What  is  the  length  of  this  section 
as  drawn?  Notice  the  formation  marked  7;  what  is  the  name  of  it?  Sup- 
pose it  restored  from  end  to  end  of  the  section,  then  measure  the  total  length 
with  scale  and  dividers;  how  much  is  it?  What  percentage  then,  did  this 


VEI^S   AND    ORES. 


177 


section  shrink  by  being  folded  as  it  is?  Point  out  here  an  anticlinal  valley. 
Point  out  a  synclinal  mountain.  What  are  the  evidences  that  this  section 
presents  a  series  of  folds?  Why  are  the  folds  not  perfect?  Why  was  not 
the  crust  mashed  into  heaps  instead  of  folded,  by  the  great  lateral  pressure? 
Did  any  of  the  folds  turn  down?  How  many  folds  might  be  produced  par- 
allel with  each  other?  Why  would  the  central  fold  be  highest?  Why  might 
not  the  sixth  fold  be  highest?  Would  the  folds  be  narrow  in  proportion  as 
they  are  low?  Should  the  rocks  mash  together  what  changes  of  temperature 
would  be  produced?  Would  the  sliding  of  one  stratum  over  another  pro- 
duce any  thermal  effects?  Would  the  bending  of  the  strata  produce  any? 
How  high  a  temperature  do  you  think  might  be  produced  by  these  mechani- 
cal actions?  Might  the  heat  be  sufficient  to  melt  the  rocks?  Suppose  there 
were  mere  pressure,  without  motion,  would  heat  be  evolved?  How  might 
metamorphism  result  from  mountain  making? 


STUDY  XXVII.  —  Veins  and  Ores. 

Let  us  return  to  the  bowlder-strewn  fields.  We  now  fix  our 
attention,  not  on  the  kinds  of  rocks,  but  on  their  structure. 
Everyone  has  noticed 
thin  sheets  of  certain 
sorts  of  rock  material 
cutting  through  a  rock  of 
some  other  sort.  In 
bowlders  these  intersect- 
ing sheets  sometimes  be- 
come very  conspicuous  in 
consequence  of  the  un- 
equal weathering  of  the 
two  kinds  of  rock.  A 
sheet  of  this  sort  is  a 
vein.  Here  is  a  notable 
specimen  in  the  museum 
of  the  University  of  Mich- 
igan. The  projecting  part 
is  a  portion  of  a  quartz- 
ose  vein  intersecting  a  mass  of  granite. 


FIG.  96. — A  QUARTZOSE  VEIN  IN  A  GRANITIC 
ROCK.  (From  a  specimen  in  the  University  of 
Michigan.) 


This  was  once  a  fragment 


178 


GEOLOGICAL    STUDIES. 


of  granite  containing  a  quartzose  vein  which  was  probably  even 
with  the  general  surface  of  the  granite.  Notice  now  how  the  vein 
projects.  That  seems  to  be  only  because  the  granite,  hard  as  it 
is,  has  weathered  away  so  much  more  than  the  vein.  Many  per- 
sons suppose  the  granite  passes  through  the  quartzose  slab,  like 
a  plug.  This  excessive  disappearance  of  the  granite  must  be  the 
effect  of  weathering;  for  any  process  of  wearing  which  would 
remove  the  granite  on  all  sides  would  also  remove  the  quartz. 
Here,  then,  is  a  Confirmation  of  the  doctrine  of  rock  weathering, 
to  which  we  were  brought  by  the  facts  considered  in  Study  XVI. 
In  our  wanderings  among  the  bowlders,  we  often  find  a  rock 
intersected  by  many  veins.  They  present 
various  forms.  Sometimes  they  are  smooth- 
sided  and  sharply  distinct  from  the  rock 
which  they  cut,  as  in  Fig.  96.  Sometimes 
they  blend  with  the  rock.  Often  they  branch 
and  pursue  zigzag  courses,  and,  splitting, 
unite  again,  inclosing  portions  of  the  rock. 
Here,  in  Fig.  97,  is  an  interesting  example, 
full  of  instruction,  but  not  at  all  infrequent. 
Study  the  forms  and  ramifications  of  these 
veins.  In  some  cases  the  different  veins  ap- 
pear to  be  but  branches  of  one  vein;  but 
what  must  we  say  of  a  rock  like  this  shown 
in  Fig.  98,  where  the  veins  are  of  different 
sorts  of  material,  and  intersect  each  other  in 
a  complex  fashion.  This  shows  a  surface  of 
syenite  on  the  beach  at  Salem,  Mass.  It  is 
thirty- six  feet  by  twenty-seven  feet.  It  was  brought  to  notice  by 
Dr.  Edward  Hitchcock  many  years  ago.  Contemplate  it  atten- 
tively. These  numerous  intersecting  sheets  are  all  veins.  But  as 
there  are  numerous  intersections,  it  is  obvious  that  an  intersecting 
vein  is  more  recent  than  one  intersected.  So  the  one  which  in- 
tersects all  the  others  is  the  last.  The  oldest  is  the  one  inter- 
sected by  all  the  others,  or  by  others  which  are  themselves  inter- 
sected by  all  the  remaining  ones,  or  by  those  which  are  finally  so 


FIG.  97. 

INTERSECTING  VEINS 
SEEN  IN  A  BOWLDER, 
ANN  ARBOR. 


VEINS   AND    ORES. 


179 


intersected.  These  veins  are  numbered,  and  you  may  exercise 
yourselves  in  showing"  that  they  are  numbered  in  the  correct  order. 
Veins  2,  5,  and  9  are  diabase;  veins  3,  4,  10,  and  11  are  of  red- 
dish granite;  vein  6,  which  is  forty  inches  wide,  is  a  porphyry, 
and  vein  7  is  also  a  porphyry;  vein  8  is  granitic.  Here  are  ten 
different  epochs  of  vein  formation.  The  syenite  mass  has  been 
rent  at  least  ten  different  times,  and  after  each  movement  some 
sort  of  vein  material  has  filled  the  fissure.  Was  the  material  in- 
jected from  below  in  a  molten  state  ?  Or  did  it  infiltrate  in  solu- 


FIG.  98.— VEINS  IN  SYENITE  ON  THE  BEACH  AT  SALEM,  MASS.     (E.  Hitchcock.) 

tion  from  the  contiguous  rock?  Or  was  it  poured  in  from  the 
top,  either  in  a  state  of  fusion  or  solution?  These  questions  pre- 
sent themselves  for  reply;  but  the  answers  are  not  obvious,  and 
we  had  better  postpone  their  consideration  till  we  get  other  facts. 
A  little  attention  will  bring  to  our  notice  veins  having  various 
contents.  Besides  the  materials  mentioned,  we  often  find  ortho- 
clase,  in  large  crystalline  masses,  filling  veins;  sometimes  calcite, 
beautifully  crystallized:  sometimes  pyrites,  or  galena,  or  blende. 
All  these  cases,  and  others,  occur  among  bowlders.  In  metallif- 


180 


GEOLOGICAL   STUDIES. 


erous  regions  it  generally  happens  that  several  different  minerals 
occur  in  one  vein  or  gangue.  They  are,  then,  sometimes  arranged 
in  alternating  layers  parallel  with  the  rock  wall,  and  each  layer 

is  called  a  comb.  In  a  regular 
combed  vein  the  combs  are  sym- 
metrically arranged  on  each  side 
of  the  centre.  This  is  shown  in 
the  annexed  Fig.  99,  where  A  A 
represent  the  country  rock,  or 
rock  formation,  holding  the  vein, 
and  the  bands  «,  b}  c,  etc.,  are  seen 
in  a  section  across  the  filling  of  the 
vein  fissure,  from  wall  to  wall. 
Here  it  appears,  that  after  the  fis- 
sure was  opened,  the  layers,  or 
combs  a,  a,  were  first  laid  on  the 
fissure  walls.  Then,  under  changed 
conditions,  the  layers  b,  b  were 
laid  upon  the  first.  Subsequently, 
with  further  changes,  the  layers 

c,  c  and  d,  d  were  deposited.  Sometimes,  as  in  the  "Three 
Princes  Vein,"  near  Freiberg,  the  number  of  combs  is  much 
greater.  This  vein,  Fig.  100,  presents  six  different  species  of 
minerals,  occurring  in  eleven  different  combs  on  each  side  of  the 
middle  —  four  of  the  sorts  being  repeated.  Examination  of  this 
diagram  will  show  the  method  of  arrangement,  and  also  the  min- 
erals of  most  frequent  occurrence  in  metalliferous  veins  or  lodes. 
Minerals  do  not  associate  themselves  together  in  lodes  in 
a  promiscuous  manner.  When  two  minerals  are  present,  they  are 
likely  to  be  galena  and  blende,  iron  pyrites  and  chalco-pyrite, 
gold  and  quartz,  cobalt  and  nickel  ores,  magnetite  and  chlorite, 
and  so  on.  If  three  minerals  are  present,  certain  rules  are  also 
observed;  and  if  more  than  three,  the  geologist  has  learned  what 
to  expect  together.  This  association  of  minerals  is  known  as 
paragenesis. 

To  illustrate  further,  in  this  connection,  some  of  the  principal 


FIG.  99. — SECTION  ACROSS  A  VEIN  FIS- 
SURE AND  ITS  CONTENTS,  SHOWING 
A  COMBED  VEIN  OF  SIMPLE  SYM- 
METHY.  (Von  Cotta.) 


VEINS   AND    ORES. 


181 


sorts  of  veins,  the  diagram,  Fig.  101,  is  annexed.     A  true  vein, 

a,  is  one  which  traverses 
a    formation    independ- 
ently of  its  texture  and 
position.  A  bedded  vein, 

b,  traverses  the  country 
parallel  to  its  stratifica- 
tion or  foliation;  but  a 
sedimentary  layer  must 
not     be     mistaken    for 
such.     A  bed  of  coal  is 
not  a  vein.      A  bedded 
vein     often     sends    out 
branches.       A     contact 
vein,  c,  occurs  between 
two     dissimilar     forma- 
tions. A  lenticular  vein, 
d,  dy  thins  out  in  all  di- 
rections.     It    must    be 
distinguished  from  len- 
ticular beds.    It  bears  no 
relation   to  the  stratifi- 
cation,  and  is,   in  fact, 

only  a  true  vein  pinched  in  two  in  several  places. 


Quartz 
Blende 

FIG.  100.— THE    "THREE   PRINCES   VEIN,"   NEAR 
FREIBERG.    (Von  Weissenbach.) 


a  C 

FIG.  101.— DIFFERENT  SORTS  OF  VEINS.    (Von  Cotta.) 


182 


GEOLOGICAL   STUDIES. 


Most  metalliferous  ores  occur  in  veins;  but  there  are  very  im- 
portant exceptions.  Many  rich  lead  mines  occur  in  crevices  or 
caverns  in  limestones,  which  are  lined  by  the  ores  of  lead  and  zinc. 
(Fig.  102.)  Placer  mining  is  a  process  of  washing  gravel  and 

sand  to  separate 
the  intermingled 
metallic  particles. 
™^  (SeeStudyXXIV.) 
The  great  beds  of 
magnetite  and 

FIG.  102.— CREYICE  IN  LIMESTONE,  SHOWING  OCCURRENCE  or    haematite     occur 
GALENA  AT  SHULLSBURG,  Wis.     (Whitney.)  mostly  in  huge  len- 

a,  Cap  Rock.    6,  Opening,  with  galena,    c,  Rock  and  detritus.    ticular  masses  con. 

formable  with  the  stratification  of  the  inclosing  schists.  The 
masses  shown  in  Figs.  103  and  104  are  portions  of  such  lens- 
shaped  beds  in  northern 

]q  New  York.     In  Figs.  105 

and  106  entire  masses  are 
shown.  Here  it  is  ap- 
parent that  the  ore  be- 
longs to  the  same  system 
of  stratification  as  the 
country  rock;  and  in  fact, 
the  lines  of  bedding  often 

pass  uninterruptedly  from  the  rock  through  the  ore.  (See  espe- 
cially Fig.  105.)  This  indicates  that  the  ore  is  segregated,  or  sep- 
arated subsequently 
to  the  deposition  of 
the  original  sedi- 
ments—  a  conclu- 
sion similar  to  that 
before  reached  in 
reference  to  certain 
concentric  struc- 
tures. (See  p.  48.) 
That  the  great  beds 


FIGS.  103  AND  104.— OCCURRENCE  or  IRON  ORE  IN 
ESSEX  COUNTY,  N.  Y.  (E.  Emmons.)  i,  Beds 
of  ore/  g,  Included  masses  of  quartz  or  other 
rock;  6,  Country  rock. 


FIGS.  105  AND  106. — LENTICULAR  MASSES  OF  IRON   ORE 
INTERSECTED  BY  LINES  OF  BEDDING.    (After  Brooks.) 

105.  Slaty,  and  blending  with  "country  rock."    Vulcan 
Mine,  near  Waucedah,  Wis. 

106.  Hard,  with  hanging  wall  of  quartz,   g,  and  "foot 
wall"  of  jasper,  ;'.    Marquette  Range,  Mich. 


VEEN'S   AND   ORES. 


183 


of  haematite  and  magnetite  were  originally  involved  in  the  sedi- 
mentary process  is  still  more  clearly  shown  in  cases  where  the 
rocks  are  less  metamorphic  and  the  ore  (generally  a  "lean"  ore) 
presents  continuous  beds  as  shown  in  Fig.  107,  H,  where  the  iron 
schists  are  conformably  interstratified  in  a  section  from  the  east- 
ern portion  of  the  Penokie  range. 

Metalliferous  deposits  are  not  to  be  sought  for  indiscrimin- 
ately. In  general,  metamorphic  rocks  are  more  productive  than 
others.  Certain  products,  also,  are  more  likely  to  occur  in  rocks 
of  certain  age.  Finally,  certain  principles  of  association  of  min- 
erals (paragenesis),  as  before  stated,  serve  as  a  clew  to  the  dis- 
covery of  particular  metals.  A  few  examples  will  illustrate  the 
distribution  of  the  metals. 


-e- 


FIG.  107.—  SECTION  THROUGH  AN  IRON  RANGE  IN  WESTERN  MICHIGAN  BETWEEN  LAKE 
GOGEBIC  AND  MONTREAL  RlVER,  SHOWING  POSITION  OF  THE  IRON  ORE,  AND  THE 
RELATIONS  OF  FOUR  SYSTEMS  OF  ROCKS.  (Pumpelly  and  Brooks.)  L,  Laurentian 
Granites,  Gneisses,  and  Schists:  H,  Huronian  Slates,  Iron  Schists,  Quartzites,  and 
Diorites;  (7,  Copper-bearing  Rocks  (Keweenian),  "South  Range";  S,  Sandstones  of 
Cambrian  Age. 

Iron  is  quite  universally  distributed.  The  great  beds  of  mag- 
netite, haematite,  franklinite,  and  titaniferous  iron  are  located  in 
the  metamorphic  strata  of  Eozoic  age.  In  America,  the  two 
former  occur  chiefly  in  northern  New  York,  northern  Michigan 
and  Wisconsin,  and  southern  Missouri.  In  Sweden  nearly  all  the 
celebrated  iron  mines  are  of  magnetite  from  Eozoic  rocks.  Titan- 
iferous iron  ore  occurs  at  many  localities  in  the  United  States, 
Canada,  Norway,  and  other  countries.  Franklinite  is  mined  at 
Hamburg,  N.  J.  Siderite  ranges  from  the  Eozoic  to  the  Carbon- 
iferous strata,  and  in  smaller  quantities  to  later  strata.  In  the 
coal  measures  of  Pennsylvania,  Ohio,  and  elsewhere,  it  occurs  as 
an  argillaceous  ore,  in  nodules,  and  beds  of  clay-iron-stone. 


184  GEOLOGICAL   STUDIES. 

Limonite  occurs  in  Mesozoic  and  more  recent  deposits;  and  also, 
as  bog  iron  ore,  in  modern  marshes;  also,  by  hydration  of  haema- 
tite, in  rocks  of  greater  age,  as  in  Salisbury,  Conn.,  and  thence 
through  Pennsylvania  and  Tennessee  to  Alabama. 

Lead,  as  galenite,  and  sometimes  lead  carbonate  or  cerussite, 
occurs  in  pockets  and  fissures  of  the  Lower  Cambrian  limestone  in 
Missouri  and  of  Upper  Cambrian  ("Galena")  limestone  in  Iowa, 
Illinois,  and  Wisconsin.  Its  mode  of  occurrence  is  shown  in 
Fig.  102,  the  cubical  crystals  of  galenite  attaching  themselves 
to  the  limestone  surfaces,  and  sometimes  attaining  a  weight  of 
sixty  to  seventy  pounds.  Galenite  also  occurs  in  veins,  in  gneiss, 
granite,  argillite,  and  crystalline  limestone,  in  various  parts  of 
Europe,  New  York,  and  New  England,  and  in  the  Carboniferous 
Limestone  of  England  and  the  continent.  Galena  is  often  worked, 
as  at  Leadville  and  in  the  Eureka  district,  for  the  silver  contained 
in  it. 

Copper  occurs  in  veins  in  metamorphic  rocks  of  Europe  and 
America.  Its  principal  ores  are  copper  pyrites  or  chalcopyrite, 
chrysocolla,  malachite,  and  azurite.  Native  copper  occurs  in  beds 
and  veins  in  the  vicinity  of  dikes  and  beds  of  igneous  origin.  In 
northern  Michigan  the  associated  rocks  are  now  thought  to  be 
of  Keweenian  age  —  that  is,  next  older  than  Cambrian.  In  New 
Brunswick,  New  Jersey,  Connecticut,  and  California,  they  are 
Mesozoic.  At  some  localities  on  Keweenaw  Point  and  in  Europe 
in  the  "  Thuringian  copper  slates,"  small  particles  are  collected  in 
large  abundance,  as  a  sort  of  drift  copper,  deposited  in  beds. 
Copper  ores  are  partial  to  chloritic  and  hornblendic  schists, 
dolorites,  and  serpentines. 

Silver  is  found  native  with  the  native  copper  of  Lake  Superior, 
and  also  elsewhere  in  veins  traversing  gneiss,  schists,  porphyry, 
and  other  rocks.  In  the  form  of  ores,  the  most  valuable  are 
argentite  or  "silver  glance,"  stephanite  (both  abundant  in  the 
Comstock  lode,  Nevada),  cerargyrite  or  "horn  silver"  (chloride) 
in  veins  of  clay  slate  in  Nevada,  Idaho,  Arizona,  and  South 
America.  Argentite  is  very  commonly  found  with  galenite. 


VEINS   AND   ORES.  185 

Silver  ores  prefer  silicious  or  argillaceous  rocks  to  limestones  or 
dolomites.  They  also  appear  to  avoid  granite  and  red  gneiss. 

Gold  is  found  only  native,  but  it  is  very  frequently  alloyed 
with  silver,  palladium,  or  rhodium.  Its  native  place  is  quartz 
veins  intersecting  metamorphic  rocks,  mostly  chloritic,  talcose, 
and  argillaceous  schists.  These  range  in  age  from  the  Eozoic  to 
the  Tertiary.  Gold  avoids  lirne.  The  breaking  up  of  the  schists 
has  caused  native  gold  to  appear  in  the  drifts  of  many  regions; 
and  from  these  most  of  the  world's  supply  has  been  obtained. 
(Study  XXIV.)  The  exhaustion  of  the  "placers,"  however,  has 
driven  miners  very  extensively  to  the  quartz  lodes  in  the  mother 
rock.  The  celebrated  Comstock  lode,  which  yields  gold  and  silver 
in  nearly  equal  proportions,  is  mostly  a  sheet  of  crushed  quartz, 
dipping  eastward  33°  to  45°,  with  a  length  of  four  or  five  miles 
and  a  maximum  thickness  of  about  six  hundred  feet.  It  has 
been  mined  to  a  depth  of  three  thousand  feet,  where  the  enormous 
outflow  of  water  is  found  to  have  a  temperature  of  170°. 

Tin  is  found,  as  cassiterite,  in  rocks  of  great  age  —  mostly 
eruptive  and  metamorphic  —  never  in  limestones  or  dolomites. 
The  world's  supply  has  come  chiefly  from  Europe;  but  mines  are 
now  worked  near  Harney,  Dak.,  and  deposits  which  promise  to 
grow  valuable  are  reported  from  Mexico,  Idaho,  Montana,  Wyo- 
ming, and  New  Mexico,  as  well  as  from  Ouster  and  other  localities 
in  Dakota. 

EXERCISES. 

Correct  this  expression :  Mr.  A.  has  a  vein  of  coal  on  his  farm.  If  Mr. 
A.  has  a  bed  of  coal,  has  he  probably  native  silver  also?  What  metalliferous 
ores  might  he  have?  What  are  the  prospects  of  a  man  exploring  for  coal  in 
dark  metamorphic  slates?  What  common  mineral  is  most  frequently  mis- 
taken for  gold  ?  Suppose  pyrite  and  gold  are  both  heated  on  a  shovel,  what 
variations  in  color  do  they  undergo?  What  is  pyrite  composed  of?  What  is 
the  source  of  the  acrid  fume  when  pyrite  is  heated?  Is  it  probable  any  gold 
could  be  found  in  your  neighbor's  garden?  Whence  comes  most  of  the  cop- 
per of  the  United  States?  In  what  form  is  it  found?  Explain  how  native 
copper  may  occur  in  the  drift  of  Ohio  or  Illinois.  Did  you  ever  hear  of  its 
occurrence  in  those  states  ?  Would  it  be  possible  for  native  silver  to  occur  at 
Columbus,  Ohio?  What  is  the  age  of  the  rocks  at  Columbus?  Would  native 


186  GEOLOGICAL   STUDIES. 

silver,  if  occurring  there,  be  found  in  the  solid  rocks  or  in  the  drift?  Look 
at  Fig.  98,  and  state  whether  vein  No.  3  was  the  first  formed  vein  there 
shown.  How  do  you  reason  on  the  subject?  Have  you  noticed  that  granite 
has  been  treated  as  a  sedimentary  rock,  and  that  here  it  appears  as  a  vein? 
Can  a  vein  be  also  sedimentary  ?  Could  this  granite  vein  be  dissolved  by  any 
means?  What  substances  may  we  conceive  in  the  water  which  saturated  this 
syenite  at  a  former  time?  Can  you  think  how  the  granite  vein  could  have 
been  deposited  through  its  walls?  Do  you  regard  it  probable  that  any  veins 
have  been  filled  by  injections  of  melted  matter? 


STUDY  XXVIII.—  Geology  of  Salt. 

Key  West  is  an  island  about  four  miles  long  and  nearly  one 
broad.  Through  the  centre,  for  two  and  a  half  miles,  extends  a 
series  of  ponds,  which  are  one  or  two  feet  lower  than  medium 
high  tides.  The  ponds  seem  to  have  been  formerly  connected 
with  the  sea,  and  to  have  been  cut  off  by  the  ridges  of  sand 
thrown  on  the  beach  by  the  waves.  The  separating  ridges, 
though  higher  than  the  ordinary  tides,  are  still  lower  than  the 
high  tides,  which  occur  twice  a  year  —  in  early  winter  and  in 
midsummer.  The  high  tides,  therefore,  flow  into  the  ponds. 
After  the  ponds  have  thus  been  filled,  or  partially  filled,  by  the 
winter  tides,  they  remain  exposed  to  the  powerful  evaporative 
influence  of  the  sun  until  the  next  midsummer.  By  this  time 
the  water  is  much  condensed.  Another  influx  of  high  tides 
restores,  perhaps,  the  volume  of  water,  but  the  resulting  brine  is 
salter,  since  no  salt  went  out  by  evaporation,  though  additional 
salt  now  comes  in.  During  another  period  of  mean  tides  a  large 
amount  of  evaporation  again  takes  place,  and  the  contents  of  the 
ponds  become  denser  than  before.  This  process  has  gone  for- 
ward before  our  eyes.  We  know  it  is  a  fact.  By  and  by  it  has 
been  repeated  so  many  times  that  the  brine  is  completely  satu- 
rated. Then,  when  the  next  high  tides  flow  in,  arid  the  next 
evaporation  follows,  the  oversaturated  brine  begins  to  deposit  its 
excess  of  salt.  The  next  year  more  salt  is  deposited.  Thus,  in 
course  of  time,  the  ponds  contain  a  supply  of  saturated  brine, 


GEOLOGY    OF    SALT.  187 

and  the  bottom  is  covered  by  a  bed  of  salt.  Now,  this  condition 
was  actually  reached  when  the  state  of  things  was  discovered  by 
the  crews  of  vessels  which  made  a  landing,  and  raked  large  quan- 
tities of  salt  from  the  ponds  and  carried  it  away.  These  things 
are  matters  of  observation.  Let  us  think  about  them. 

Suppose  some  large  bay  or  gulf  should  become  cut  off  from 
the  ocean,  so  as  to  have  communication  with  it  only  at  high 
tides.  Suppose,  for  instance,  it  should  be  the  Red  Sea.  Then, 
if  the  evaporation  during  the  year  were  greater  than  the  supply 
of  fresh  water  from  the  inflowing  streams  and  the  clouds,  each 
year's  evaporation  would  increase  the  density  of  the  water.  If, 
occasionally,  through  high  tides,  or  extraordinary  storms,  there 
should  be  a  fresh  influx  of  sea  water,  the  amount  of  salt  eventu- 
ally introduced  into  the  basin  would  become  indefinitely  great, 
and,  crystallization  of  salt  having  at  length  begun,  the  amount 
deposited  would  increase  until  the  conditions  should  change. 
Some  sediment,  more  or  less,  would  find  its  way,  also,  into  the 
sea,  and  would  mingle  with  the  precipitated  salt.  The  sea 
would  thus  be  gradually  filled  up.  It  is  supposable  that  the 
obstruction  at  the  straits  might  finally  increase  until  all  access  of 
the  Indian  Ocean  should  be  prevented.  This  might  result  from 
an  elevation  of  the  region  about  the  straits.  The  filling  of  the 
basin  would  now  be  completed,  chiefly  by  fragmental  deposits. 
Or  if,  before  the  filling  of  the  basin,  a  subsidence  should  be  expe- 
rienced, a  new  influx  of  the  ocean  would  bring  new  beds  of  sedi- 
ments over  the  salt  accumulations  precipitated  and  buried  in  a 
previous  age.  If,  instead  of  subsidence,  or  if,  after  a  period  of 
subsidence  and  sedimentation,  there  should  be  an  elevation  of 
the  region,  then  it  would  become  a  part  of  the  land.  We  have 
already  learned  that  events  of  this  nature  have  taken  place  again 
and  again  in  the  history  of  the  world. 

Suppose  we  stand  upon  that  land.  There  are  beds  of  salt 
under  us.  If  we  dig  down,  we  shall  sooner  or  later  reach  them. 
These  salt  beds  were  once  the  bottom  of  the  sea.  We  may  find 
more  or  less  pure  salt;  but  we  shall  certainly  find,  also,  the 
mechanical  sediments  which  were  borne  into  the  sea  while  the 


188  GEOLOGICAL   STUDIES. 

salt  was  crystallizing,  and  after  the  salt  had  ceased  to  crystallize. 
We  shall  find,  also,  everything  which  was  originally  in  the  sea 
water. 

What,  now,  shall  we  conclude  when  we  see  men  digging  salt 
from  the  earth  in  the  county  of  Chester,  near  Liverpool  ?  Here, 
at  Northwich  and  Winsford,  after  penetrating  through  gypseous 
clay  120  feet,  beds  of  rock  salt  are  found  sixty  to  ninety  feet 
thick.  Beneath  these  are  indurated  clays  for  thirty  or  forty  feet, 
containing  beds  of  rock  salt,  and  below  these,  100  feet  more  of 
rock  .salt.  Much  of  this  salt  is  earthy,  but  some  is  quite  pure. 
The  salt  is  dissolved,  often  in  sea  water,  arid  then  evaporated  in 
pans  by  artificial  heat.  This  is  what  we  see  going  on  at  the 
surface.  Are  we  not  led  to  conclude  that  here,  in  Cheshire,  is  a 
salt  formation  quite  similar  to  the  one  which  we  supposed  formed 
in  the  Red  Sea  ?  When  we  look  about,  we  see  Cheshire  lying  in 
a  geological  trough,  bounded  by  the  hills  of  Yorkshire  on  the 
northeast,  and  the  highlands  of  Wales  on  the  southwest.  The 
formation  filling  the  trough  is  the  Triassic.  We  can  understand 
that  that  valley  was  once  a  bay  projecting  inward  from  the  At- 
lantic Ocean,  and  was  probably  filled  precisely  as  we  have  sup- 
posed of  the  Red  Sea. 

We  may  subject  this  conclusion  to  severer  tests.  If  we  take 
a  portion  of  sea  water  and  evaporate  it,  we  find  precipitated  suc- 
cessively peroxide  of  iron  (not  in  all  cases),  gypsum,  common 
salt,  and  epsom  salts,  or  magnesium  sulphate.  Calcium,  mag- 
nesium, and  potassium  chlorides  remain.  If  we  take  the  natural 
brine  from  a  well  in  Cheshire  or  Syracuse,  and  evaporate  it,  the 
same  succession  of  precipitates  is  obtained.  The  peroxide  of 
iron  is  thrown  down  in  the  "  clearing  vats."  The  gypsum  forms 
the  first  crust  on  the  bottoms  of  the  kettles  or  pans.  The  com- 
mon salt  is  next  crystallized  out  (in  part),  and  the  chlorides 
remaining  form  the  "  bitterns."  Examining  more  closely  one  of 
the  salt  formations — for  instance,  the  Salina  —  we  find  in  the 
lower  beds  some  ferruginous  clays;  above  these,  gypseous  clays, 
and  clays  with  masses  of  gypsum  arranged  in  horizontal  courses; 
still  higher,  supplies  of  brine,  and  in  many  districts,  vast  beds  of 


GEOLOGY   OF   SALT.  189 

rock  salt.  Still  above  are  limestones  with  acicular  cavities,  which 
seem  to  have  been  once  occupied  by  needles  of  epsom  salts. 
Here  is  a  close  correspondence,  and  on  these  evidences  we  may 
rest  our  theory  of  the  origin  of  salt  formations. 

The  theory  is  not  intended  to  apply  to  cases  where  salt  is  con- 
fined to  a  vein  or  dike,  as  at  Bex,  in  Switzerland.  Sometimes, 
undoubtedly,  streams  have  been  fed  by  brine  springs  issuing  from 
older  formations,  and,  discharging  into  inland  lakes  without  out- 
lets, have  undergone  evaporation  and  produced  new  salt  forma- 
tions. Some  of  the  salt  lakes  of  our  western  territories  probably 
have  an  origin  of  this  sort;  but  their  remote  origin  was  in  the 
sea  water  which  salted  the  salt  formations  which  now  surround 
or  underlie  them.  The  Caspian  and  Aral  seas,  however,  are  un- 
doubtedly remnants  of  the  ancient  ocean;  and  when  they  disap- 
pear, salt  formations  will  occupy  their  sites.  The  process  is 
already  far  advanced  in  many  of  the  bays  of  the  Caspian  and  the 
outlying  lakes  along  its  borders. 

Turn  once  more  to  the  geological  map,  page  118,  and  fix  atten- 
tion on  the  formations  stretching  east  and  west  through  central 
New  York.  They  all  dip  southward,  or  away  from  the  Eozoic  of 
Canada.  We  once  constructed  a  section  from  Canada  to  Pennsyl- 
vania (Fig.  53),  which  shows  this  dip,  but  greatly  exaggerated. 
Now,  the  Salina  group,  which  is  the  great  salt  formation  of  New 
York,  occupies  a  position  in  the  upper  part  of  the  Silurian,  as  you 
must  remember  (see  Fig.  39).  The  Helderberg,  which  holds  a 
place  above  it,  is  almost  wanting  in  central  New  York,  and  con- 
sequently the  outcrop  of  the  Salina  at  Syracuse  is  close  by  the 
lowest  Devonian  —  that  is,  the  Oriskany  sandstone  and  the  Cor- 
niferous.  Its  place  may  be  marked  on  the  section  Fig.  53. 

Now  let  us  make  a  section  on  a  larger  scale  for  the  purpose  of 
showing  more  clearly  the  geological  position  of  the  brines  ob- 
tained at  Syracuse  and  worked  under  the  auspices  of  the  state 
for  about  a  hundred  years  (Fig.  108).  Here  we  see  the  Salina 
formation  excavated  at  its  outcrop.  The  excavation  has  become 
filled  with  drift  materials.  A  depression  remained  in  the  drift 
which  permitted  a  shallow  lake  to  exist  for  a  geologic  period; 


190 


GEOLOGICAL   STUDIES. 


but  this  has  now  shrunken  to  the  present  Onondaga  Lake  which 
is  bordered  on  the  south  by  a  marsh.  Beyond  the  marsh  is  the 
hard  ground  on  which  Syracuse  is  built;  and  beyond  this  rises  a 
hill  underlaid  by  the  Corniferous  and  Onondaga  limestones.  On 
the  slope  of  the  hill  may  be  found  some  outlying  fragments  of 
the  Oriskany  sandstone.  Now,  the  brine  which  saturates  some 
portions  of  the  Salina  strata,  overflows  at  the  border  of  the  form- 
ation, and  saturates  the  bed  of  drift  material  filling  the  excava- 
tion just  mentioned.  The  rains  falling  on  the  surface  rest  on  the 
top  of  the  denser  brine,  instead  of  settling  down,  and  the  sur- 
plus flows  into  Onondaga  Creek.  Accordingly,  the  wells  dug  in 


FIG.  108.— GEOLOGY  OF  THE  SYRACUSE  BRINES.  SECTION  ACROSS  THE  ONONDAGA  SALT 
BASIN  AT  SYRACUSE,  N.  Y.  c,  Corniferous  Limestone;  0,  Oriskany  Sandstone;  A, 
Ilelderberg  Group ;  w,  Brine  Wells. 

the  saturated  drift  receive  a  supply  of  brine;  and  the  deepest  ones 
obtain  the  strongest  brine.  These  are  about  400  feet  deep. 

Notice  that  the  brine  supply  is  merely  an  overflow  from  the 
formation,  and  must  be  comparatively  weak  and  limited  in 
amount.  But  notice  that  the  formation  to  the  south  of  Syracuse 
sinks  to  a  greater  depth.  From  this  it  may  be  inferred  that  arte- 
sian borings  some  miles  south  would  reach  stronger  supplies,  and 
perhaps  even  a  bed  of  rock  salt.  Farther  west,  in  Wyoming 
county,  experiments  of  this  kind  have  disclosed  the  existence  of 
large  supplies  of  native  salt. 

Referring  to  the  map  again,  it  will  be  seen  that  the  Silurian 
passes  in  a  basin  slope  under  the  peninsula  of  Michigan  and  lakes 


GEOLOGY   OF   SALT. 


191 


Huron  and  Michigan.  The  Salina  which  lies  near  the  top  of  this, 
outcrops  on  the  east,  at  Grand  River  in  Ontario;  on  the  west,  at 
Milwaukee;  on  the  north,  at  Mackinac  and  on  the  south,  at  San- 
dusky.  This  basin  retains,  therefore,  all  its  ancient  salinity. 
Accordingly  salt  borings  carried  to  the  appropriate  depths  in  almost 
any  part  of  the  peninsula,  reach  either  abundant  strong  brine  or 
a  thick  bed  of  salt.  The  diagram  Fig.  109,  illustrating  these 
relations,  shows  a  gradual  increase  in  the  depth  of  the  salina 
basin,  as  we  approach  the  centre  of  the  peninsula.  The  salina 
formation  is  productive  on  the  eastern  and  western  borders,  and 
on  the  northeast  in  the  Huron  peninsula,  and  at  Alpena  on  Thun- 
der Bay. 


VIII 


FIG.  109  —GEOLOGY  OF  MICHIGAN  BRINES.  (Vertical  Scale  much  exaggerated.)  Form- 
ations indicated  by  numerals  (see  Table,  Pt  II.  ch.ii).  11,  Huron  Group,  consisting 
of  Gencsee  Shale,  Portage  and  Chemung;  12, Marshall  Sandstone;  13a,  Michigan  Salt 
Group;  14a,  Parma  Sandstone  (Coal  Conglomerate).  Geological  Positions  of  Brine 
Wells:  7,  St.  Clair  Group;  77,  Port  Austin  Group;  777,  Manistee  and  Muskegon;  77, 
Original  Well,  Plaster  Quarries;  F,  Grand  Rapids;  VI,  Lansing  (last  three  unproduc- 
tive) ;  F77,  Saginaw  Valley;  F7/7,  Bay  City,  shallow  wells;  7A",  Ann  Arbor  Artesian 
Boring,  755  feet  (no  result). 

But  the  characteristic  salt  formation  of  this  state  is  the 
"  Michigan  Salt  Group",  which  constitutes  the  lower  part  of  the 
Carboniferous  Limestone  (see  Fig.  39),  and  whose  position  is  shown 
in  the  preceding  diagram.  This  basin  underlies  the  greater  part 
of  the  peninsula.  As  the  strata  are  too  compact  to  permit  the 
extensive  accumulation  of  brine,  the  brine  sinks  into  the  underly- 
ing sandstone,  known  as  the  "  Marshall  Sandstone,"  and  indicated 
in  the  "  Geological  Column  "  as  the  probable  equivalent  of  the 
"  Catskill  Group  "  at  the  bottom  of  the  Carboniferous  System  — 
or  as  many  think,  at  the  top  of  the  Devonian.  The  densest 
brine,  as  in  other  cases,  is  somewhat  remote  from  the  out- 


192  GEOLOGICAL   STUDIES. 

cropping  border  of  the  Marshall  reservoir,  though  the  line  of 
outcrop  is  marked  by  a  circle  of  salt  springs.  This  basin  sup- 
plies the  celebrated  wells  along  the  valley  of  the  Saginaw  River. 
No  native  salt  is  known  to  exist  in  the  Michigan  Salt  Group,  and 
it  is  apparent  that  the  brine  will  eventually  become  exhausted. 
The  group  contains  enormous  deposits  of  beautiful  gypsum.  This 
exists  in  a  continuous  stratum  from  side  to  side  of  the  penin- 
sula. It  shows  again  the  same  association  with  salt  as  occurs  in 
sea  water. 

Still  another  salt  basin  is  formed  in  Michigan  by  the  Coal 
Measures.  The  brine  accumulates  in  the  underlying  "  Parma 
Conglomerate."  (See  Figs.  39  and  109.)  The  shallow  wells  at 
Bay  City,  on  the  Saginaw  River,  are  supplied  from  this  source. 
The  generally  saliferous  condition  of  the  formations  in  Michigan 
seems  to  depend  on  their  dish-like  conformation.  As  a  result  of 
this,  they  have  retained  most  of  the  soluble  constituents  left  in 
them  by  the  ancient  sea  water.  There  are  even  indications  that 
a  productive  salt  basin  exists  between  the  Salina  and  the  Mar- 
shall sandstone,  in  the  so-called  "  Huron  Group,"  which  embraces 
the  "  Chemung  "  of  Fig.  39.  These  strata  are  everywhere  satu- 
rated with  brine  and  "bitterns";  and  they  supply  the  numerous 
"  mineral  wells  "  of  the  state. 

Strata  belonging  to  the  horizon  of  the  Michigan  salt  group 
are  similarly  productive  of  brine  and  gypsum  in  Nova  Scotia  and 
New  Brunswick.  The  brine  accumulations  in  Ohio  seem  to  be  in 
the  Waverly  sandstone;  those  of  Kentucky  are  in  the  "knob- 
stones,"  and  those  of  Tennessee  are  in  the  "  silicious  group." 
These  are  all  the  geological  equivalents  of  the  Marshall  sand- 
stone. 

Other  salt  deposits  of  the  western  United  States  are  found  in 
the  Cretaceous.  The  salt  and  gypsum  deposits  at  and  near  Salt- 
ville,  in  Washington  county,  Va.,  are  thought  by  Stevenson 
to  be  not  older  than  Tertiary.  The  salt  is  from  200  to  500  feet 
thick,  mingled  with  some  red  clay;  and  the  gypsum  occurs  in 
detached  masses,  enwrapped  in  the  clay.  The  basins  are  exca- 
vated along  a  fault  which  has  brought  Lower  Carboniferous  and 


GEOLOGY   OF   SALT.  193 

Cambrian  formations  into  juxtaposition.  The  singular  formations 
at  Petite  Anse,  La.,  are  probably  also  Tertiary  or  Post-Tertiary. 
Most  of  the  salt  formations  of  Europe  are  in  different  members 
of  the  Triassic.  Those  of  Russia  are  in  the  Permian;  those  of  the 
Austrian  Alps,  in  the  Jurassic;  those  of  the  Pyrenees  and  of  Car- 
dona,  in  the  Cretaceous;  while  those  of  Wielicza,  in  Galicia,  of 
Tuscany  and  Sicily,  are  Tertiary.  Salt  also  occurs  as  a  volcanic 
product.  The  borings  at  Stassfurt,  Germany,  have  penetrated 
1,066  feet  of  Triassic  rock  salt,  and  at  Sperenberg,  5,084  feet, 
without  reaching  the  bottom.  The  Stassfurt  salt  manufacture  is 
important. 

EXERCISES. 

If  the  Mediterranean  is  salter  than  the  open  sea,  how  can  the  fact  be 
explained?  If  the  Black  Sea  were  not  salter  than  the  Atlantic,  how  might 
the  fact  be  explained?  Why  is  it  necessary  to  redissolve  the  salt  found 
native  in  Cheshire,  England?  What  caused  the  clayey  state  of  some  of  the 
salt?  Was  the  salt  deposited  as  a  sediment?  How  might  gypseous  deposits 
occur  above  salt  beds  as  well  as  below?  What  is  the  cause  of  the  rusty  stain 
seen  in  some  inferior  samples  of  salt?  What  causes  the  moist  condition  of 
some  inferior  salt?  Would  pure  salt  be  best  obtained  by  slow  evaporation, 
or  by  rapid?  Will  you  explain  why?  What  position  of  the  strata  is  most 
favorable  for  retaining  their  brine  ?  What  position  is  favorable  for  getting 
the  salt  leached  out?  Draw  a  diagram  showing  how  a  salt  formation  might 
become  destitute  of  brine.  In  boring  a  salt  well,  would  veins  of  fresh  water 
sometimes  be  passed?  How  could  fresh  water  be  prevented  from  running 
down  and  mixing  with  the  brine?  Suppose  the  Michigan  salt  basin  full  of 
brine;  where  would  the  surface  level  stand?  Could  the  brine  be  anywhere 
higher  than  the  border?  Suppose  the  border  deeply  notched  on  one  side, 
where  would  the  surface  level  of  the  brine  be?  Is  the  surface  of  the  land 
above  or  below  the  probable  surface  level  of  the  brine  in  that  basin?  If 
higher,  will  the  brine  then  rise  to  the  level  of  the  land?  (See  Fig.  109.) 
Why  could  not  a  brine  well  be  a  flowing  well?  May  the  water  from  a  flow- 
ing well  be  brackish?  Draw  a  diagram  explaining  your  view.  In  a  fresh- 
water artesian  well  must  we  also  have  a  basin  arrangement?  Would  a  flow- 
ing well  be  possible  with  a  basin  arrangement?  Suppose  the'  rock  arrange- 
ment for  a  flowing  well  such,  for  instance,  as  supplies  Chicago  (Fig.  55), 
should  be  filled  with  brine,  would  we  not  have  a  flowing  well  of  salt  water? 
Would  it  last  indefinitely?  What  would  it  become,  and  why?  Why  must  a 
flowing  well  be  a  well  of  fresh  water?  Then  how  can  we  have  a  permanent 
flowing  mineral  spring? 


194  GEOLOGICAL   STUDIES. 


STUDY  XXIX.— Geology  of  Petroleum. 

At  the  mouth  of  Thunder  Bay,  of  Lake  Huron,  is  a  little 
island  known  as  Sulphur  Island.  It  rises  but  a  few  feet  above 
the  level  of  the  water,  and  its  surface  is  strewn  with  a  deep  bed 
of  water-worn  fragments  of  black  bituminous  shale  (see  Study 
XI,  and  especially  XIII).  A  few  years  ago  some  fishermen  built 
a  camp  fire  on  the  the  bed  of  shale,  and  the  shale  itself  took  fire 
and  burned  deep  into  the  ground,  and  continued  to  burn  for  some 
months.  The  pieces  of  shale  were  not  reduced  to  ashes,  but  re- 
tained their  form.  The  bituminous  matter  burned  out  and  they 
were  left  with  a  reddened  appearance.  Indeed  the  bitumen  was 
seen  to  fry  out  of  the  heated  fragments  and  become  ignited. 
Near  by,  on  the  main  land,  is  a  solid  bed  of  this  shale,  and  there 
are  some  fossils  in  it  which  we  have  found  nowhere  except  in  the 
"  Genesee  Shale"  at  the  top  of  the  Hamilton  Group  (Fig.  39). 
Now  this  Genesee  Shale  extends  from  Central  New  York  into  all 
our  western  states.  The  observation  at  Sulphur  Island,  and  sim- 
ilar ones  elsewhere,  suggest  that  the  formation  contains  an  enor- 
mous supply  of  bituminous  matter.  Bituminous  matter  is  not 
always  exactly  the  same.  It  is  everywhere  composed  of  carbon, 
hydrogen  and  a  little  oxygen.  Carbon  and  hydrogen  combine  in 
many  different  proportions  to  form  hydrocarbons.  Some  of  the 
compounds  are  solid  or  tarry,  some  are  liquid  and  some  are  gase- 
ous. Examples  of  these  are  asphaltum,  coal  tar,  kerosene,  naph- 
tha, benzole,  illuminating  gas  (Study  XIII).  The  bituminous 
matter  which  heat  expels  from  the  Genesee  Shale  is  a  mixture  of 
several  of  these.  What  we  call  kerosene,  then,  is  contained  in 
Genesee  Shale. 

Reasoning  in  this  wav,  the  enterprise  was  instituted  some 
years  ago,  of  extracting  burning  oil  from  black  shales.  It  was 
successfully  done  at  Dartmoor  in  England,  Autun  in  France  and 
Biihl  in  Prussia.  It  was  much  more  successfully  done  in  Breck- 
enridge  county,  Kentucky,  from  cannel  coal,  which  is  only  a  black 
shale  peculiarly  rich  in  carbon  and  hydrogen.  It  can  be  done 


GEOLOGY    OF    PETROLEUM.  195 

with  greatest  success  from  certain  substances  known  as  Torbanite, 
Albertite  and  Grahamite.  But  all  undertakings  of  this  class  were 
rendered  profitless,  about  1859,  by  the  discovery  of  enormous 
supplies  of  natural  oil  on  Oil  Creek,  in  Pennsylvania;  and  afterward 
in  many  other  regions.  This  natural  oil,  or  petroleum,  is  essen- 
tially a  bitumen.  It  consists  of  several  hydrocarbons  mixed. 
In  different  localities,  it  is  light,  or  amber-colored  or  dark;  it  is 
thin,  or  dense,  or  tarry,  according  to  the  proportions  of  the 
lighter  and  heavier  compounds.  It  closely  resembles  the  sub- 
stance obtained  from  black  shales  by  artificial  distillation.  Is  it 
possible  the  native  petroleum  comes  also  from  black  shales 
through  a  process  of  natural  distillation  ?  Let  us  examine  the 
circumstances.  In  western  Pennsylannia,  the  oil  is  found  accu- 
mulated in  porous  sandstones  some  hundreds  of  feet  below  the 
surface.  They  are  in  part,  at  least,  sandstones  of  the  Chemung 
Group.  Below  them  lies  the  very  same  Genesee  Shale  before 
referred  to  (see  Fig.  III).  Should  that  undergo  a  process  of  dis- 
tillation, the  products  being  lighter  than  water  would  rise  through 
the  water-saturated  rocks  to  some  formation  in  which  it  could 
not  escape.  Suppose  the  depth  to  be  800  feet;  is  it  allowable  to 
assume  the  temperature  at  that  depth  sufficient  to  promote  a  dis- 
tillation, however  slow  ?  In  our  judgment  it  is  allowable. 

Let  us  examine  the  situation  in  other  localities.  At  Oil 
Springs  and  other  points  in  Ontario,  oil  has  long  been  obtained 
by  boring  through  surface  clays  into  the  Hamilton  limestone  —  a 
depth  of  one,  two,  or  three  hundred  feet.  This  is  quite  below  the 
Genesee  Shale.  But  there  lies  at  the  bottom  another  and  very 
similar  black  shale,  called  the  Marcellus.  So  the  same  kind  of  a 
source  is  present  as  in  Pennsylvania.  But  instead  of  a  porous 
sandstone  here  to  serve  as  a  reservoir,  we  have  the  shattered  and 
cavernous  limestone;  and  the  clayey  covering  of  drift  shuts  it  in 
(Fig.  110,  II). 

But  we  find  in  Ontario  another  quality  of  oil,  derived  from 
another  source.  In  the  same  township  are  wells  which  consist  of 
shafts  sunken  through  the  drift  to  the  rock,  and  these  obtain  a  dark 
and  tarry  petroleum,  which  is  used  for  lubricating  purposes  (see 


196 


GEOLOGICAL   STUDIES. 


Fig.  110).  The  diagram  shows  the  Genesee  Shale  above  the  Hamil- 
ton Limestone  extending  under  the  region  of  these  wells.  This  be- 
comes the  source  of  oil  which  rises  into  the  gravel  bed  at  the  bottom 
of  the  drift  and  saturates  it,  and  thence  flows  into  the  well.  But 
the  oil  undergoes  some  evaporation  in  consequence  of  the  par- 
tially pervious  character  of  the  drift,  and  hence  appears  more 
tarry  than  the  oil  from  greater  depths.  Both  situations  here 
favor  our  conjecture.  Let  us  turn  to  West  Virginia. 

Here  we  find  ourselves  over  the  Coal  Measures;  and  find  like- 
wise, two  situations  in  which  petroleum  accumulates.  First,  we 
get  the  principal  accumulation  in  what  probably  answers  to  the 
Conglomerate  (Fig.  Ill),  and  we  find  below,  a  series  of  Sub-Con- 
glomerate Coal  Measures,  which  are  indicated  in  Fig.  39.  These, 


i     ii 


FIG.  110. — GEOLOGY  OF  PETROLEUM  IN  ONTARIO.  (7,  Corniferous  Limestone;  3/,  Marcel- 
lus  Shale;  //.Hamilton  Limestone;  G,  Genesee  Shale;  D,  Drift,  with  gravel  at 
bottom  and  impervious  clay  above.  /,  "Surface  Well"  at  Oil  Springs;  //,  Com- 
mon bored  wells ;  111,  Test  well,  bored  600  feet. 

like  the  true  Coal  Measures,  contain  strata  of  dark  bituminous 
shale.  The  Sub-Conglomerate  Shales  are,  therefore,  in  the  precise 
position  to  answer  the  same  purpose  as  the  similar  Genesee  and 
Marcellus  Shales  in  the  other  cases.  Oil  also  accumulates  in  the 
Conglomerate  in  southwestern  Pennsylvania,  southeastern  Ohio 
and  northeastern  Kentucky. 

Secondly,  we  find  some  oil  accumulated  in  the  sandstones  of 
the  proper  Coal  Measures.  Some  of  the  interstratified  black 
shales  lie  beneath  the  horizon  of  oil  accumulation,  and  are,  there- 
fore, in  position  to  yield  oil  by  distillation,  which  may  rise  into 
the  sandstones. 

On  the  Cumberland  River,  in  southern  Kentucky,  many  years 


GEOLOGY    OF    PETROLEUM.  197 

ago,  in  boring  for  salt,  a  large  supply  of  oil  rushed  forth.  The 
situation  here  is  on  the  Trenton  Group  of  the  Cambrian.  (Fig. 
39.)  When  we  come  to  a  detailed  examination  of  this  group,  we 
find  the  upper  half  of  it  (Cincinnati  sub-group)  composed  of 
shales,  marls,  and  limestones.  In  New  York  the  divisions  of  this 
sub-group  are  named  Hudson  River  Slate  above  and  Utica  Shale 
below;  and  the  latter  is  described  as  "a  dark-colored  slate  fre- 
quently loaded  with  carbon"  (Mather),  and,  indeed,  often  igno- 
rantly  explored  for  coal.  Now,  wherever  this  condition  of  the 
lower  part  of  the  Cincinnati  sub-group  exists,  we  have  the  same 
provision  as  before  for  the  evolution  of  petroleum.  On  the 
Great  Manitoulin  Island  of  Lake  Huron  a  small  amount  of  oil 
has  also  been  obtained  from  the  Cincinnati  sub-group. 

In  the  neighborhood  of  Glasgow,  Ky.,  some  petroleum  has 
been  obtained.  The  locality  is  on  the  shattered  and  cavernous 
Carboniferous  Limestone;  and  the  fluid  accumulates  in  the  fis- 
sures, as  in  the  fissures  of  the  Hamilton  Limestone  of  Ontario. 
Underneath  we  find  some  silicious,  dark-colored  shales,  and  below 
these  the  widespread  Genesee  Shale  full  of  hydrocarbonaceous 
matter,  as  elsewhere.  (Fig.  111.) 

In  this  survey  of  the  facts  we  find  that  oil  accumulation  sus- 
tains no  uniform  relation  to  deposits  of  coal.  The  oil  is  not 
derived  from  coal.  The  situation  in  every  oil  region,  except 
West  Virginia,  is  geologically  below  the  coal,  and  geographically 
remote  from  coal.  Nor  do  we  find  in  beds  of  coal  any  exudation 
of  oily  matter,  while  in  black  shales  we  generally  find  it.  In 
Carbonaceous  Shales  the  hydrocarbons  manifest  a  predisposition 
to  form  and  escape.  Mixture  of  aluminous  matter  with  the  car- 
bon may  be  the  predisposing  cause.  Beds  of  carbon  nearly  free 
from  argillacous  matter  do  not  undergo  the  change. 

We  should  not  overlook  the  fact  that  many  limestones  — 
especially  the  Corniferous  and  the  Niagara  —  are  in  some  regions 
densely  charged  with  bituminous  matter.  This  fact  has  led  to  the 
opinion  that  the  source  of  the  oil  is  in  limestones  rather  than 
black  shales.  Accordingly,  a  "test  well"  was  bored  at  Oil 
Springs,  Ont.,  six  hundred  feet  deep,  and  the  Corniferous  Lime- 


198  GEOLOGICAL   STUDIES. 

stone  was  penetrated  (Fig.  110),  but  without  any  additional  sup- 
ply of  oil.  The  same  limestone  has  been  many  times  penetrated 
in  Ohio  and  Michigan,  but  no  supply  was  ever  reached.  The 
tarry  Niagara  Limestone  was  bored  into  in  Chicago,  but  artesian 
water  was  obtained  instead  of  a  supply  of  oil.  (Fig.  55.) 

It  seems  reasonable  now  to  infer,  from  the  uniform  relations 
of  the  facts,  that  some  carbonaceous,  shaly  formation  is  always 
the  source  of  the  petroleum,  and  that  it  is  eliminated  from  this 
by  a  slow  process  of  spontaneous  distillation,  under  the  influence 
of  such  temperatures  as  exist  within  the  crust  of  the  earth. 

The  following,  then,  are  the  conditions  of  oil  accumulation  in 
quantities  of  commercial  importance: 

1.  A  source  below,  from  which  the  oil  is  elaborated.     This 
we  find  from  observation  to  be  always  a  bituminous  shale. 

2.  A  reservoir  above,  in  which  the  oil  is  accumulated.     This 
is  a  sandstone,  or  a  shattered  limestone,  or  shale. 

3.  A  slightly  anticlinal  position  of  the  reservoir,  to  prevent 
the  lateral  spread  and  wastage  of  the  oil. 

4.  An  impervious  covering,  to  prevent  the  escape  of  the  oil 
to  the  surface  and  volatilization  there. 

If  the  reservoir  is  wanting,  the  presence  of  the  shale  is  un- 
availing. If  the  anticlinal  is  crowned  by  a  break,  it  may  result 
in  the  escape  of  the  oil.  In  the  course  of  ages  the  volatilization 
of  the  light  hydrocarbons  may  leave  a  fissure  filled  with  the  solid 
residue.  Thus  is  formed  the  Grahamite  of  West  Virginia,  and 
also  the  Albertite  of  Nova  Scotia.  If  the  impervious  covering  is 
wanting,  the  oil  may  rise  to  the  surface,  and  a  residue,  like  that 
forming  the  "gum  beds"  at  Oil  Springs,  Ont.,  will  be  deposited; 
or,  on  a  larger  scale,  extensive  beds  of  asphaltum  will  remain,  as 
in  Santa  Barbara  and  Los  Angeles  counties,  Cal. ;  on  the  islands 
of  Cuba  and  Trinidad,  in  the  West  Indies;  in  Egypt,  Palestine, 
and  other  countries.  The  Egyptian  asphalt  has  for  centuries 
been  famous  for  its  useful  qualities,  and  .is  extensively  used  in 
Europe  for  streets.  California  asphaltum  also  finds  extensive 
use. 

Let  us  now  bring  the  facts  together  in  a  tabular  exhibit: 


GEOLOGY  OF  PETROLEUM. 


199 


CONSPECTUS  OF  THE  GEOLOGY  OP  PETROLEUM. 


FORMATIONS.  SOURCE   OF   OIL. 


DRIFT  GRAVEL  (10)  (c) 

SANDSTONES  (9) 
Bituminous  Shales  (f) 

COAL  MEASURE  SANDSTONES  (8)         (e) 
Coal  Measure  Shales  (e) 
COAL  CONGLOMERATE  (7)  (d)  (c)  (b) 

Shales  and  Shaly  Coals  (d) 

CARBONIFEROUS  LIMESTONE  (6)         (c) 
WAVERLY  SANDSTONE  (5)  (c) 

CHEMUNG  SANDSTONE  (4)  (c) 


GENESEE  SHALE  (3) 
Genesee  Shale  (c) 

HAMILTON  LIMESTONE  (2)  (b) 

Marcellus  Shale  (b) 

Corniferous  Limestone 
Niagara  Limestone 

FISSURED  SHALT  LIMESTONE  (1)        (a) 
Black  Utica  Shales  (a) 


OIL   REGIONS. 

Oil  Springs,  Ont, 

Cal.,  in  Los  Angeles  County, 
etc. 

West  Va.  ;  Southwest  Pa. 

South  west  Pa.  ;  W.  Va.;  North- 

east Ky. 

Glasgow  region,  Ky.  (part.) 
Contiguous  part  of  Tenn. 
Central  O.  ;  Venango  Co.,  Pa. 

Northwest  Pa.;    Southern  N. 
Y.  ;  Northeast  O. 


E.     Glasgow  region,  Ky.  (part) 


D.    Bothwcll,  Ont. 
C.    Enniskillen,  Ont. 


Bituminous  generally. 
Bituminous  frequently 

B.    Manitoulin  Island. 
A.    Burksville,  Ky. 


Here  the  various  formations  concerned  are  arranged  in  geo- 
logical order.  Those  which  serve  as  the  source  of  petroleum  in 
America  are  printed  in  italics;  those  which  serve  as  reservoirs, 
in  small  capitals.  The  letters  (a),  (b),  (c),  etc.,  are  used  to  des- 
ignate sources;  the  numerals  (1),  (2),  (3),  etc.,  denote  reservoirs, 
and  the  letters  A,  B,  C,  etc.,  indicate  regions. 

The  foregoing  facts  are  otherwise  set  forth  graphically  in  the 
accompanying  diagram,  Fig.  111.  Petroleum  is  known  to  exist 
to  some  extent  in  all  formations  from  the  Eozoic  to  recent  de- 
posits. 

Other  important  localities  of  petroleum,  besides  those  men- 
tioned, are  Baku,  on  the  western  border  of  the  Caspian,  in  Geor- 
gia, Rangoon,  Burmah,  and  the  duchies  of  Parma  and  Modena,  in 


200 


GEOLOGICAL   STUDIES. 


Italy.  It  is  also  very  recently 
reported  from  Deli,  on  the 
east  coast  of  Sumatra,  one 
well  yielding  270  barrels  a 
day.  The  Baku  petroleum  oc- 
curs in  a  porous,  argillaceous 
sandstone  of  Tertiary  age. 
In  the  vicinity  are  hills  of 
volcanic  rocks,  through  which 
springs  of  the  heavier  sorts 
flow  out.  The  Rangoon  oil 
is  obtained  from  wells  sunk 
sixty  feet  in  beds  of  sandy 
clay,  which  rest  on  sandstones 
and  argillaceous  slates.  Un- 
der the  slates  is  said  to  be 
"  coal,"  but  the  strata  are 
probably  of  Tertiary  age,  and 
the  coal  is  likely  to  be  an 
argillaceous  lignite  or  a  bitu- 
minous shale.  In  Los  An- 
geles and  neighboring  coun- 
ties, Cal.,  the  yield  from  Ter- 
tiary strata  was  5,000,000 
gallons  in  1882,  and  262,000 
barrels  in  1884. 

Illuminating  oil  may  be  ob- 
tained from  all  organic  sub- 
stances by  distillation.  Petro- 
leum is  probably  derived  from 
both  animal  and  vegetable 
remains.  That  occurring  in 
limestones  may  be  of  animal 
origin,  but  that  derived  from 
black  shales  more  probably 
has  a  vegetable  origin. 


GEOLOGY    OF   PETROLEUM.  201 

The  production  of  natural  gas  in  1885  and  subsequently  has 
grown  to  a  wonder  not  inferior  to  the  yield  of  petroleum  which 
began  in  1859.  It  escapes  from  wells  bored  in  certain  districts, 
generally  1,500  to  2,000  feet  deep.  The  gas  is  a  varying  mix- 
ture of  light  and  heavy  carburetted  hydrogens  —  chiefly,  however, 
marsh  gas  —  and  escapes  generally  under  the  very  high  pressure 
of  100  to  700  pounds  to  the  square  inch.  In  the  vicinity  of 
Pittsburgh,  not  less  than  150,000,000  cubic  feet  were  produced 
daily  in  the  latter  part  of  1885,  and  60,000,000  were  already 
introduced  into  the  city.  Sixty-five  to  seventy  millions  were 
daily  wasting  in  the  Murraysville  district  alone.  Gas  fuel  has 
already  revolutionized  the  manufactures  of  the  city.  It  is 
reported,  also,  that  pipes  are  being  laid  for  conveyance  of  the 
gas  to  Buffalo  and  Cleveland.  Meantime,  enormous  supplies  of 
gas  have  been  reached  in  northern  Ohio  from  wells  which  seem 
to  penetrate  the  Cambrian.  One  is  located  at  Cleveland.  At 
Fremont,  it  is  said,  2,000,000  feet  were  (in  January,  1886) 
yielded  daily.  Gas  and  oil  are  reported  at  Lima,  at  the  depth  of 
1,251  feet.  The  "  Great  Karg  Well,"  at  Findlay,  Ohio,  is  reported 
(April,  1886)  to  yield  10,000,000  feet  daily  from  a  depth  of 
1,144  feet.  The  ignited  jet  ascends  115  feet. 

It  is  impossible  that  such  enormous  supplies  of  oil  or  gas 
should  continue  many  years.  Reproduction  is  undoubtedly  in 
progress,  but  it  is  comparatively  slow.  We  are  using  and  wast- 
ing the  accumulations  of  millions  of  years. 

EXERCISES. 

When  black  shale  burns  with  a  flame,  why  does  it  not  crumble  to  ashes 
like  coal?  What  causes  the  reddened  appearance  of  burned  shales?  Name 
some  localities  where  oil  springs  occur.  Can  you  tell  why  Paint  Creek,  in 
Kentucky,  is  so  named?  Is  the  vicinity  of  an  oil  spring  the  best  place  to 
bore  for  oil?  If  not,  why  not?  Does  mineral  pitch  dissolve  in  water? 
What  causes  the  durability  of  asphaltum  when  used  for  pavements?  What 
are  the  characters  of  lubricating  oil?  Can  you  describe  the  odor  of  the 
Ontario  oils?  Why  is  kerosene  sometimes  called  "coal  oil"?  What  is 
Breckenridge  oil?  What  sort  of  coal  is  found  in  Breckenridge  county? 
How  does  it  differ  from  a  bituminous  or  carbonaceous  shale?  Would  there 


202  GEOLOGICAL   STUDIES. 

be  a  good  prospect  of  success  in  seeking  an  oil  well  at  Ontonagon,  Lake 
Superior?  Look  over  this  list  of  localities,  and  indicate,  as  nearly  as  you  can, 
those  most  favorably  situated  for  oil  wells,  and  those  least  favorably  situated : 
Potsdam,  N.  Y. ;  Hartford,  Conn. ;  Waukesha,  Wis. ;  Mobile,  Ala. ;  Chatta- 
nooga, Tenn. ;  Binghamton,  N.  Y. ;  St.  Clair,  Mich. ;  Erie,  Penn. ;  Wheel- 
ing, W.  Va. ;  Frankfort,  Ky. ;  Montreal,  P.  Q. ;  Sarnia,  Ont.  Have  you 
carefully  considered  what  formations  underlie  these  places?  Have  you  indi- 
cated the  oil-producing  formations  under  them  ?  Have  you  indicated  forma- 
tions suited  to  serve  as  reservoirs?  Some  mineral  "gum "  (asphaltum)  occurs 
on  the  surface  west  of  Grand  Traverse  Bay,  Mich. ;  explain  how  this  happens. 
How  do  the  formations  underlying  St.  Clair,  Mich.,  compare  with  those 
under  Oil  Springs,  Ont.  ?  If  they  are  the  same,  why  cannot  oil  be  obtained 
at  St.  Clair?  What  would  seem  to  be  the  source  of  the  powerful  gas  wells 
in  Knox  county,  Ohio?  As  12,000  feet  of  gas  are  estimated  to  be  equivalent 
in  heating  capacity  to  one  ton  of  bituminous  coal,  how  many  tons  are  repre- 
sented by  a  total  supply  at  Pittsburgh  of  60,000,000  feet?  How  many  coal 
miners  does  this  supply  of  gas  represent? 


STUDY  XXX.— Examination  of  Some  Cup  Corals. 

Rocks  and  minerals  are  not  the  only  geological  specimens 
brought  to  our  very  doors  in  the  Drift.  Every  one  living  in  the 
western  states,  or  in  southern  Ontario,  is  acquainted  with  certain 
organic  forms  (compare  Study  XVIII)  which  the  untaught  farmers 
refer  with  amusing  confidence  to  things  familiar  to  them.  Thus 
we  have  "petrified  honeycomb,"  "petrified  wasps'  nests,"  "pet- 
rified horns,"  "  petrified  butterflies,"  "  petrified  snakes  "  —  not  to 
mention  "petrified  hands,"  "petrified  feet,"  and  other  petrified 
things,  which  are  nothing  but  curious  results  of  the  weathering 
of  rocks.  We  must  try  to  make  some  acquaintance  with  these 
objects.  At  present  we  will  look  into  their  structure,  and  here- 
after we  will  ascertain  what  formations  they  are  derived  from. 
It  is  common  to  find  a  promiscuous  assemblage  of  these  forms 
gathered  on  some  shelf  or  in  some  box,  badly  cared  for,  and  yet 
too  curious,  and  often  too  beautiful,  to  permit  the  intelligent 
owner  to  throw  them  away.  Often  he  longs  to  know  something 
about  them;  but  there  are  really  few  available  aids  within  his 
reach. 


EXAMINATION    OF   SOME   CUP   CORALS.  203 

Now,  let  us  look  over  such  a  collection.  Most  of  these  fossils 
are  worn  —  some  too  much  worn  to  possess  value,  but  others 
showing  at  least  some  little  part  in  a  fine  state  of  preservation. 
In  fact,  some  of  the  finest  specimens  ever  found  come  from  the 
Drift  deposits.  Large  and  valuable  collections  may  be  gathered 
from  this  source,  in  any  part  of  the  region  west  of  the  Hudson 
River.  Assorting  these  specimens  according  to  such  knowledge 
as  we  possess,  we  easily  divide  them  into  specimens  which  seem 
to  be  shells  and  specimens  which  seem  to  be  corals,  or  which,  at 
least,  are  not  shells.  Among  those  which  appear  to  be  corals  we 
readily  make  again  another  distinction.  Those  which  present 
any  resemblance  to  honeycomb  or  wasps'  nests  may  be  separated 
from  those  which  are  more  or  less  horn-shaped  —  that  is,  short, 
conical  and  curved,  like  a  young  steer's  horn.  In  picking  out  all 
of  this  division,  we  must  consider  that  most  are  somewhat  broken 
and  worn,  and  we  must  try  to  conceive  the  shape  of  the  missing 
parts.  We  must  also  make  allowance  for  some  irregularities  of 
form.  These  corals  are  not  all  shaped  precisely  like  bullocks' 
horns,  even  when  perfect.  Sometimes  they  are  rather  long  and 
cylindrical;  sometimes  they  are  suddenly  bent  one  way  or  another; 
and  often  they  swell  out  and  contract  at  intervals.  Sometimes 
the  exterior  appears  to  be  covered  by  a  skin;  often  this  has  been 
worn  off,  and  we  see,  externally,  white  lines  imbedded  in  the 
coral  mass,  and  running  from  end  to  end.  This  is  the  division  of 
the  corals  which  we  wish  to  study.  These  are  cup  corals.  A 
group  of  them  is  shown  in  Figs.  112-116.  These  are  several  of 
the  best  preserved. 

First,  study  their  external  characters.  The  whole  specimen 
is  sometimes  called  the  cell.  It  is  also  know  as  polypary.  You 
notice  at  the  larger  end,  which  we  will  call  the  upper  end,  a 
depression,  giving  the  coral  the  appearance  of  a  cup.  This  is 
called  the  calyx,  or  cup  (plural,  calyces],  and  this  explains  why 
these  are  called  cup  corals.  (Figs.  113,  114,  116.)  The  adjec- 
tive which  expresses  some  relation  to  the  cup  is  calyc' inal,  as 
calycinal  extremity.  Sometimes  we  find  a  pit  in  the  bottom  of 
the  cup  on  one  or  two  sides,  as  in  Fig.  113.  This  is  a  fossa, 


204 


GEOLOGICAL   STUDIES. 


fossette,  or  fovea.  The  exterior  of  a  perfect  specimen  is  gen- 
erally covered  by  a  skin-like  covering  called  epi-the'ca.  This, 
in  some  species,  is  smooth,  but  more  frequently  it  is  transversely 
wrinkled.  (Fig.  112.)  Under  the  epitheca  is  the  wall.  Where 
the  epitheca  is  wanting,  or  has  been  worn  off,  we  often  see 


FIGS.  112-116.— CUP  CORALS.  112,  Zaphrentis  Prolifica,  exterior.  113,  Same,  showingthe 
Cup.  114,  Amplexus  Shumardi,  general  view.  115,  Clislophyllum  Oneidaevse,  show- 
ing interior.  116,  Cyathophyllum  Cornicula. 

numerous  white  lines  running  lengthwise  of  the  coral  (Fig.  124); 
these  are  cos' toe,  or  ribs  (adjective,  costal).  In  the  cup  may  be 
seen  a  set  of  radiating  raised  lines,  which  look  like  the  upper 
edges  of  radial  plates.  These  extend  from  the  outer  wall  toward 
the  centre.  Different  species  differ  greatly  in  the  extent  of  their 
development.  These  are  generally  called  sep'ta  (singular,  sep- 


EXAMINATION   OF   SOME   CUP   CORALS.  205 

turn).  We  shall  see  that  they  run  lengthwise  toward  the  lower 
end  of  the  polypary. 

Next,  let  us  study  the  interior.  To  do  this  we  may  make  a 
transverse  section  —  that  is,  a  cut  across  the  polypary  at  right 
angles  with  the  axis  or  line  through  the  middle,  from  end  to  end. 
You  will  be  much  interested  in  this  work.  Sometimes  we  find  a 
specimen  broken  square  across,  but  often  we  must  break  it.  The 
surest  way,  to  avoid  spoiling  the  specimen,  is  first  to  file  a  groove 
around  the  fossil  with  a  three-cornered,  or,  better,  a  "  knife- 
edge,"  file.  But  you  must  select  a  calcareous  specimen;  a  silici- 
fied  one  would  ruin  your  file  immediately.  Then  resting  the 
coral  on  a  solid  support,  like  an  anvil,  if  you  have  one,  place  the 
edge  of  a  "cold  chisel"  in  the  groove,  and  strike  a  smart  blow  on 
it  with  a  hammer  or  mallet.  If  the  pene  of  your  geological  ham- 
mer is  not  very  dull,  you  can  use  that  as  a  cold  chisel.  Now 
grind  one  of  the  broken  surfaces  flat  and  smooth,  and  polish  it. 
You  may  use  first  the  smooth  flat  side  of  a  grindstone;  or  you 
may  use  emery  and  water  on  a  flat  surface  of  lead,  copper  or  iron. 
Next,  you  may  polish  the  surface  on  a  fine  hone;  or  you  may  do 
it  with  emery  flour  on  a  piece  of  plate  glass  six  or  eight  inches 
square.  The  finest  polish  may  be  produced  with  dry  emery 
"  slime "  on  a  piece  of  buckskin  tacked  to  a  smooth  board. 
When  a  transverse  section  of  your  cup  coral  is  thus  polished,  it 
shows  a  beautiful  internal  structure  which  you  can  examine  with 
a  lens,  and  of  which  you  may  make  drawings. 

But  it  is  possible  to  do  even  better  than  this.  You  may 
procure  a  very  thin  transverse  slice  —  so  thin  that  light  passes 
through  it,  and  the  whole  internal  structure  will  be  perfectly 
shown.  File  a  deep  groove  around  the  specimen,  a  quarter  of 
an  inch  back  from  the  polished  face,  and  cautiously  chip  off  this 
thick  slice.  Attach  it  to  a  piece  of  thick  glass,  one  or  two  inches 
square,  by  melting  on  the  glass,  over  a  lamp  or  a  stove,  some  hard- 
ened Canada  balsam,  pressing  the  slice,  polished  side  down,  in 
the  balsam,  till  the  air  bubbles  are  expelled.  When  cold  and 
hard,  grind  the  rough  side  as  before,  holding  by  means  of  the 
glass,  until  as  thin  as  paper,  or  thinner  if  still  too  opaque,  and 


206 


GEOLOGICAL   STUDIES. 


polish  the  surface.  Then  soften  the  balsam  and  cautiously  push 
the  slice  off  into  a  few  drops  of  softened  or  liquid  balsam  resting 
close  by  on  a  microscopic  glass  slide,  taking  care  to  exclude  air 
from  beneath  the  specimen.  A  microscopic  slide  is  a  piece  of 
glass,  one  by  three  inches.  Next,  cover  the  slice  with  a  drop 
of  balsam,  and  put  on  a  thin  glass  cover  seven-eighths  of  an  inch 
square,  which  may  be  held  down  by  means  of  a  spring  "  clothes- 
pin," until  the  balsam  is  hard.  If  the  balsam  was  liquid  before 
warming,  gentle  heat  will  now  be  required  to  harden  it.  Finally, 
superfluous  balsam  should  be  removed  with  a  knife,  and  the  final 
cleaning  of  the  surfaces  of  the  glass  effected  with  spirits  of  tur- 
pentine and  bits  of  cotton  cloth.  There  is  nothing  in  all  this 
beyond  the  skill  or  resources  of  any  intelligent  student;  but  the 
result  will  be  found  both  gratifying  and  instructive.  Thin  slices 
of  rocks  and  minerals  may  be  similarly  prepared;  but  silicious 
specimens  make  more  laborious  manipulation,  and  it  is  best  to 
begin  with  thin  chips  struck  off  with  a  hammer.  If  thin  slices 
of  corals  are  not  made,  many  polished  surfaces  should  be  prepared. 
Now,  what  does  a  thin  section  of  our  cup  coral  reveal  ?  Here 
it  is,  in  Fig.  117.  You  notice,  first,  the  outer  wall.  Next,  you 
see  a  system  of  radiated  structures, 
extending  from,  the  wall  toward  the  cen- 
tre. Make  a  transverse  section  at  any 
distance  from  the  bottom,  and  similar 
structures  will  be  seen.  These,  then, 
are  the  septa  before  noticed  in  the  cup. 
They  are  longitudinal  radiating  plates. 
Some  of  the  septa,  as  you  perceive, 
SEC-  extend  well  toward  the  centre,  and  in 
CUP  CORAL  this  species  are  a  little  twisted  together. 
Some  extend  but  a  part  of  the  distance. 
This  coral  which  is  shown  in  Fig.  117 
has  also  a  fovea  in  the  cup  —  though  your  specimen  may  not  be 
sufficiently  perfect  to  show  it. 

Now,  think   over  the  characters   just  mentioned.     You  may 


Fig.    117.— TRANSVERSE 
TION    OF 
(Zaphrentis        prolifica}, 
SHOWING  THE  SEPTA. 


EXAMINATION   OF   SOME   CUP   CORALS. 


207 


remember  that  this  assemblage  of  characters  forms  the  genus 
called  Zaphrentis. 

Let  us  take  another,  and  different,  cup  coral,  and  prepare  a 
longitudinal   section.     This   may  be  done   in   a   manner  entirely 
similar  to  that  before  described.     Grooves  will  be  filed  length- 
wise of  the  specimen  along  opposite  sides.     Then,  after  polishing 
one  of  the  halves  and  attaching  to  the  glass, 
it  may  be  best  to  grind  away  the  whole  half 
down  to  a  thin  slice.     Sometimes  we  use  a 
large  file  for  coarse  work.      Here  is  the  result, 
in  Fig.   118.     The   outer  wall   is,  of  course, 
shown  as  before.     If  the  section  is  precisely 
central,  none  of   the    septa  will  be  cut,  and 
hence  none  will  be  seen.     Here  are  no  septa 
shown;    but    some   transverse    structures   are 
seen.     These  are  called  floors  or  tabulae,  for 
they  are  thin,  more  or  less  flat  plates.     By 
some  they  are  called  diaphragms  and  septa 
— but  we  will  not  so  use  these  terms.     Notice 
that   in  this    specimen  the  tabulae  are  broad 
and  conspicuous,  extending  almost  from  wall 
to  wall   of   the  body  cavity.      Here,  in  Fig. 
119,  is  a  cross  section  of  a  specimen  of  the  same  species.     Notice 
particularly  that  the  septa  are  very  narrow.     Bear  in  mind  this 
combination  of  characters.     It  is  known  as  the 
genus  Amplexus. 

Now  we  shall  find  no  difficulty  in  preparing 
transverse  and  longitudinal  sections  of  many 
different  specimens.  In  Figs.  120  and  121  we 
have  sections  of  a  form  which  shows  septa  not 
reaching  the  centre,  and  tabular  occupying  only 
the  middle  of  the  cavity,  stretching  from  the 
inner  margins  of  the  septa  on  one  side  to  the 
inner  margins  on  the  other.  This  portion  of  the 
interior  is  known  as  the  central  part  of  the  vis- 
ceral cavity^  or  simply  as  the  visceral  cavity. 


FIG.  118 — LONGITUDI- 
NAL SECTION  OP  A 
CUP  CORAL  (Amplex- 
us Yandelli),  SHOW- 
ING THE  TABULAE. 
Defects  in  tabulae  re- 
sult from  fossiliza- 
tion. 


FIG.  119. 


CROSS  SECTION  op 
THE  SAME  SPECIES 
AS  IN  FIG.  118, 
SHOWING  VERY 
NARROW  SEPTA. 
See  also  Fig.  115. 


208 


GEOLOGICAL   STUDIES. 


FIG.  ICO.— TRANSVERSE 
SECTION  OF  ANOTHER 
CUP  CORAL  (Cyatho- 
phyl'um),  SHOWING 
SEPTA,  CENTRAL 
AREA,  AND  DISSEPI- 
MENTS IN  THE  PERI- 
PHERAL REGION.  (Di- 
agram.) 


FIG.  121.— LONGIUTDI- 
NAL  SECTION  OF  A 
SPECIMEN  OF  THE 
SAME  SPECIES  AS  IN 
FIG.  120  (Cyathophyl- 
lum). 


But  we  notice  in  the  section  (Fig.  120)  some  delicate  structures 
passing  from  septum  to  septum,  in  the  region  outside  of  the  cen- 
tral part  of  the  visceral 
cavity,  and  dividing  it 
into  small  cell-like  com- 
partments. This  is  known 
as  the  peripheral  region, 
and  these  delicate  divid- 
ing lines  are  sections  of 
dissepiments.  These  run 
obliquely  downward  and 
inward,  as  shown  in  Fig. 
121,  and  seem  to  be  modi- 
fications of  tabulae.  You 
will  notice  particularly 
what  characters  are  asso- 
ciated together  in  this  form.  They  constitute  the  genus  Cya- 
thophylhim. 

Now  let  us  pause  to  gather  these  few  results  together,  and 
make  some  tentative  generalizations.  The  fundamental  structures 
of  cup  corals,  as  we  have  seen,  belong  to  three  categories:  (1) 
The  mural  system,  or  outer  wall;  (2)  the  septal  system,  or  radi- 
ating vertical  plates  or  lamellae;  (3)  the  tabular  system,  or  trans- 
verse plates.  Let  us  conceive  these  three  systems  to  be  essential 
structures  in  every  cup  coral,  and  to  be  always  present  in  some 
state  of  development,  or  under  some  modification;  and  let  us  con- 
ceive a  tabula  to  be,  theoretically,  a  floor  extending  across  the 
whole  body  cavity,  from  wall  to  wall.  Then  we  shall  have  some 
interesting  studies  in  tracing  the  homologies  of  these  parts  in 
different  genera  —  that  is,  in  determining  what  structures  should 
be  referred  to  septa  and  what  to  tabulae,  and  what  is  the  nature 
of  the  modification  undergone  by  these  categories  respectively  in 
any  particular  case.  If  these  assumptions  are  not  in  accordance 
with  fact,  we  shall  be  unable  to  interpret  cup-coral  structures  on 
the  basis  of  them. 

We  must  be  prepared  to  find  each  of  these  categories  devel- 


EXAMINATION   OF   SOME   CUP   CORALS.  209 

oped  to  a  complete  extent,  to  a  partial  extent,  or  only  to  an  in- 
cipient extent;  or  even,  in  some  cases,  they  may  be  obsolete,  that 
is,  only  potentially  present.  If  the  tabular  extend,  under  any 
modification,  quite  across  the  body  cavity,  they  must  intercept  all 
the  septa,  so  that  the  wedge-shaped  space  between  each  two 
septa  will  be  cut  into  a  number  of  narrow,  wedge-shaped  spaces 
arranged  in  a  vertical  series.  If  the  outer  parts  of  the  tabulae 
are  curved  upward,  instead  of  continuing  horizontal,  then,  on  a 
transverse  section  like  Fig.  120,  they  will  be  cut,  and  their  cut 
edges  will  be  seen  exposed.  From  this  will  result  the  appearance 
of  cellular  tissue  seen  in  the  peripheral  region  of  the  Cyathophyl- 
lum,  Fig.  120.  So  we  may  anticipate  other  modifications  of  the 
several  parts. 

EXERCISES. 

If  your  place  of  study  is  anywhere  west  of  the  Hudson  River,  the  Adiron- 
dacs  and  the  Appalachians,  and  east  of  the  Missouri  River,  and  not  on  a 
prairie-covered  region,  you  should  make  a  collection  of  Drift  fossils.  In  this 
is  included  nearly  the  whole  valley  of  the  St.  Lawrence  River  and  the  penin- 
sula of  western  Ontario;  but  we  exclude  the  Eozoic  regions  of  northern 
Michigan,  Wisconsin,  and  Minnesota,  and  southern  Missouri.  Of  course, 
fossils  found  in  place  (in  the  rock)  must  be  had  when  obtainable,  though 
really  Drift  fossils  often  show  structures  more  perfectly  than  these.  Have 
you  collected  any  fossils?  Have  you  attempted  to  arrange  them  according 
to  their  forms  and  characters?  Take  this  lot  of  fossils  before  us  and  arrange 
them  as  completely  as  possible.  Point  out  the  cup  corals.  Take  any  specimen 
and  state  what  part  is  broken  away.  What  has  been  the  effect  of  wear  on  it? 
Is  it  silicified  or  calcareous?  Show  where  a  transverse  section  might  be  cut. 
Show  the  longitudinal  section.  Does  this  specimen  show  the  septa?  Does  it 
show  any  tabulas?  Is  the  epitheca  present?  Does  the  peripheral  part  con- 
tain cellular  structure?  What  genus  has  this  character?  Do  the  septa 
extend  to  the  centre?  Take  other  specimens  and  answer  the  same  questions 
in  reference  to  them. 


210 


GEOLOGICAL   STUDIES. 


STUDY  XXXI.— Further  Examination  of  Cup  Corals. 

Let  us  seek  further  facts  by  examining  a  genus  of  cup  corals 
known  as  Streptelasma.  In  Fig.  122  we  have  a  view  of  the 
usual  appearance  of  the  exterior,  and  Fig.  123  shows  the  cup 
with  a  fovea  on  one  side,  and  a  series  of  septa  reaching  the  centre 
with  somewhat  of  a  twist.  There  is  no  appearance  of  cellular 
tissue  in  the  peripheral  part,  and  there  is  no  indication  of  tabulae 
except  in  the  partially  cellular  mass  in  the  centre,  which,  in  some 


122 


FIGS.  122-124.— VIEWS  OF  SEVERAL  CUP  CORALS. 

122.  Streptelasma  corniculum,  exterior.     123.   Same,  showing  Cup.    124.   Same,  showing 
arrangement  of  Septa  on  the  exterior. 

cases,  we  find  raised  into  a  dome-like  elevation.  This  central 
mass  may  be  conceived  as  resulting  from  the  intersections  and 
slight  twisting  of  tabulae  and  septa.  In  Fig.  124  we  find  an 
interesting  exhibition  of  an  arrangement  of  the  septa  often 
called  "feather-form  "  or  pinnate.  The  lines  show  where  the 
septa  come  to  the  periphery,  the  external  wall  in  this  case  being 
deficient. 

This  example  will  serve  to  show  the  mode  of  increase  of  the 
septa.  A  section  across  Fig.  124  close  to  the  lower  end  would 
reveal  only  four  septa.  These  are  the  primary  septa.  A,  J2,  C, 
Z>,  Fig.  125.  Of  these,  A  and  C  are  shown  in  Fig.  124.  A  is 
the  chief  septum,  J2  the  antiseptum,  and  C  and  D  the  lateral 
septa.  With  the  growth  of  the  coral,  four  additional  sopta 


FURTHER    EXAMINATION"   OF   CUP   CORALS.  211 

appear,  in  the  places  marked  1,  1,  1,  1,  in  Fig.  125.     Two  of  these 

are  parallel  with  J?,  one  parallel  with 

C,  and    one  with  D.     Of  these  four 

additional    septa,    the    one    parallel 

with   C  is  skown  in  Fig.  124.     With 

further  growth,  these  septa  elongate, 

and  others  appear  parallel  with  them,      PlGs.~125i  12G._PRIMITIV~   SEPTA 

as   may   be   seen  at  2,  2,  2,  2,   Fig.         OF  A  CUP  CORAL  (MUCH  EN- 

126,  and  in  part,  also,  in  Fig.  124.      19*A™ED)W 

125.  The  Four  Primary  Septa,  A, 

Thus,  as  growth    proceeds,  and  the         B,  c,  D,  with  the  First  Acces- 
circumference  of  the  cup  increases,      «J!OIZB?e«t*'  *'  *' *'  *' 

126.  The  Second  Set  of  Accessory 

the  distance  01  the  septa  in  the  cup         Septa,  2,  2,  2,  2. 

appears  to  remain  the  same.    Now  let         The   numerical   designation   of 

.  .         Septa  is  the  same  as  in  Fig.  127. 

us  conceive  the  exterior  ot  the  speci- 
men, Fig.  124,  to  be  a  skin,  and  let  us  slit  down  along  the  pri- 
mary septa,  A,  J3,  C,  D,  to  the  apex.  Then,  removing  the  skin 
and  spreading  it  on  a  flat  surface,  we  shall  see  the  plan  of  the 
septa  and  their  mode  of  growth.  The  appearance  will  be  some- 
what as  shown  in  Fig.  127.  Here  A,  J2,  C,  and  D  indicate  the 
places  of  the  primary  septa,  as  before.  It  is  seen  that  the  whole 
system  is  divided  into  four  quadrants  or  fascicles  of  septa  —  the 
two  fascicles  on  the  right  of  the  median  line  A  JB  being  sym- 
metrical with  the  two  fascicles  on  the  left.  The  plan  of  the  septa 
is,  therefore,  fundamentally  bilateral.  The  radiality  is  subordi- 
nate—  and  this,  it  may  be  said,  can  be  shown  of  every  other  so- 
called  "radiate"  animal.  The  break  or  discontinuity  of  the  septa 
along  the  primary  septum  A  is  called  the  apertural  gap.  The 
one  opposite,  along  J3,  is  the  central  gap"  the  other  two  are  the 
lateral  gaps.  The  place  of  the  principal  fovea  in  the  cup  is  at 
A.  Giving  attention  to  each  quadrantal  fascicle  in  succession,  it 
is  easy  to  perceive  the  succession  of  the  septa.  The  older  ones 
are  the  longer,  because  they  have  been  growing  a  longer  period. 
The  shorter  septa  are  the  newer  ones.  The  succession  is  indi- 
cated by  the  numerals  1,  2,  3,  4,  5,  6,  etc.  Had  the  cell  grown 
further,  the  additional  septa  would  have  been  introduced  at 
0,  0,  0,  0.  Since  four  is  the  number  of  primary  septa  in  the 


212 


GEOLOGICAL   STUDIES. 


cup  corals,  they  are  also  known  as  TETRACOBALLA.     By  Milne- 
Edwards  they  were  styled  JKugosa. 


Apertural  Gap 


0 


Central  Gaf 

B 

FIG.  127. -PLAN  OF  SEPTA  AND  BILATERAL  ARRANGEMENT  OF  A  CUP  CORAL. 
The  external  walls  of  the  the  four  Fascicles  of  Septa  are  developed  or  spread  out 
into  one  plane.    The  additions  to  the  number  of  Septa  take  place  at  0,  0,  <9,  0.    All  the 
Septa  increase  in  length. 

After  examining  the 
cups  of  numerous  cup  cor- 
als, we  shall  find  that  the 
plan  of  septa  above  de- 
scribed is  but  imperfectly 
shown  in  the  cup;  yet  in- 


dications of  it  almost  al- 
A  very  clear 


FIG.  128.— CUP  OF  Meno- 
phyllum,  E  &  H. 


FIG.  129.— PLAN  OF  SEP- 
TA IN  Zaphrentis  Ida,  ways  exist. 

WIN.    FROM  ROCK-  illustration  of  it  is  given 

FORD,  IND.  (From]S"at-  .      _. 

we.)  m  Fig.  128. 


FURTHER   EXAMINATION    OF   CUP   CORALS. 


213 


In  some  of  the  western  states,  and  even  western  New  York 
and  Ontario,  we  can  hardly  make  a  collection  from  the  Drift  with- 
out finding  included  some  corals  of  the  species  represented  in 
Figs.  130,  131.  Here  we  have  a  widely  open  cup,  showing  septa 
almost  strictly  radiate,  but  with  the  alternate  septa  shorter  than 
the  others.  It  was  probably  this  beautifully  rayed  appearance 
which  suggested  to  Milne-Edwards  the  name  Heliophyllum. 
The  transverse  section,  Fig.  132,  shows  a  vesicular  tissue  in  the 
peripheral  region,  and  this  is  nearly  all  the  evidence  of  the  pres- 
ence of  a  tabular  system.  Both  figures,  however,  reveal  certain 


FIG.  131. — SAME,  VIEW  OP 
THE  CUP. 


FIG.  132,— PART  OF  TBANS- 
VEBSE  SECTION  OF  Helio- 
phyllum Halli. 


FIG.  130.-  Heliophyllum 
Halli,  HAMILTON 
GROUP,  WIDDER,  ONT. 
(From  Nature.) 

appendages  to  the  septa  which  are  conceived  to  be  characteristic 
of  this  genus,  though,  in  fact,  we  find  them  in  several  other 
genera.  A  longitudinal  section,  Fig.  133,  shows  them  to  be 
sharply  raised,  opposite  pairs  of  cari'nce,  or  ridges,  running  along 
the  lateral  surfaces  of  the  septa,  and  curving  in  such  a  way  as  to 
outcrop  in  the  cup.  The  carinae  are  seen  in  Fig.  133,  in  places 
(7,  (7,  where  the  thin  section  cuts  obliquely  across  a  septum. 

An  equally  common  form  of  cup  coral  is  the  Cystiphyllum, 
Americanum,  Fig.  134.  The  cup  presents  a  surface  covered 
with  blister-like  elevations;  and  sections  in  Figs.  135,  136  and 


214 


GEOLOGICAL   STUDIES. 


137   show    the    whole    interior    occupied    by   a    coarse    vesicular 
tissue,  without  characteristic  septa  or  tabulae.     We  may  suppose 

the  mutual  intersections  of 
these  structures  have  re- 
sulted in  such  mutual  dis- 
placement and  distortion 
that  the  typically  wedge- 
form  compartments  have  be- 
come mere  vesicles. 

All   the  cup  corals  thus 
far    examined     are     simple. 
That  is,  each  specimen  is  the 
FIG ;.  188.-LONGITUDINAL  SECTION  OP  Heliophyl-  k      f  j       j     individual 

lum  Halhi  SHOWING   THE  CARIN^E  ON  THE 

SEPTA.  (From  Nature.)  <7,  (7,  Carinse  cut  polyp.  But  many  cup  corals 
lengthwise,  the  oblique  sections  of  the  Septa  are  compound,  and  we  find 
giving  the  clouded  patches.  T7,  coarse  cellu- 
lar tissue  of  central  part  of  visceral  cavity,  f,  them  so  in  the  Drift, 
fine  cellular  tissue  of  peripheral  part.  (The  Throughout  the  Northwest, 
black  blotches  are  mere  opaque  rock  mate-  3 

one  01  the  very  commonest 

and  most  beautiful  of  these 
is  Acervularia  Davidso?ii 
(Figs.  138,  139).  Visitors  to 
Petoskey  on  Little  Traverse 
Bay  are  made  very  familiar 
with  this  coral  through  the 
polished  specimens  which  are 
offered  for  sale.  But  it  is 
found  there  imbedded  in  its 
natural  formation.  Acervula- 
ria forms  aggregations  in 
elegant  spheroidal  and  cake- 
like  masses.  Each  mass  is  a 
group  of  small,  generally 
crowded,  and  polygonal  cells, 
each  of  which  is  a  real  cup 
coral.  They  are  mostly  six- 
sided  by  mutual  pressure,  but  sometimes  a  tube  stands  sufficiently 


rial.) 


FIG.  134. — Cystiphyllum  Americanwn.  UP- 
PER EXTREMITY  OF  A  LARGE  SPECIMEN. 
(From  Nature.) 


FURTHER   EXAMINATION   OF   CUP   CORALS. 


215 


isolated  to  retain  its  fundamental  cylindrical  form.  The  com- 
mon wall  between  contiguous  cells  is  delicately  wavy.  The 
centre  of  each  cup  is  abruptly  sunken.  The  septa  of  first  order 
reach  the  centre; 
those  of  the  sec- 
ond order  reach 
only  to  the  cen- 
tral pit.  Indica- 
tions of  carinae 
are  seen  on  the 
septa  in  the  pe- 
ripheral region. 
In  the  cross-sec- 
tion, Fig.  139,  the 


characters  of  the 


FIG.    135.  —  PART    OP   TRANS- 
VERSE SECTION  OF  Cystiphyl- 
limiting  wall  and       lum     Americanum.      (From 
Nature.) 


FIG.  136.  —  TRANSVERSE  SEC- 
TION OF  A  Cystiphyllwn, 
SHOWING  A  DENSE  ZONE 
AROUND  THE  CENTRAL.  PART, 
AND  COARSER  TISSUE  IN  THE 
CENTRE.  (From  Nature.) 


the  septa  are  still 

more  clearly  shown.     It  appears  from  this  that  carinae  are  not 

exclusively  characteristic  of  Heliophyllum  ;  but  they  make  here 

a  different  group  of  characters  from  the 

group  which  constitutes  a  Cyathophyl- 

lum. 

In  Fig.  140  we  have  another  com- 
pound cup  coral.  Each  cell  or  tube  is 
by  itself  nearly  a  Cyathophyllum. 
That  is,  it  shows,  in  longitudinal  sec- 
tion, some  very  distinct  though  irregu- 
lar tabulae  in  the  central  portion,  and 
an  elegant  vesicular  tissue  in  the  pe- 
ripheral portion.  But  the  tabulae  rise 
in  a  conical  elevation  in  the  centre  of 
the  cup,  constituting  the  distinct  genus  Fm  137._LoN0IT0DINAL  SEC- 
LithostTOtion.  TION  OF  Cystiphyllum  Ameri- 

.  canum.    (From  Nature.) 

Still  another  elegant  compound  cup 

coral  appears  in  Figs.  141,  142  and  143.     The  genus  Diphyphyl- 
lum  is  characterized  by  the  presence  of  an  inner  wall,  which  is 


216 


GEOLOGICAL   STUDIES. 


here  very  distinctly  shown.  In  addition,  notice  the  delicate 
equidistant  tabulae  across  the  small  inner  tube,  and  the  fine  vesi- 
cular tissue  between  it  and  the  outer  wall.  The  septa  are  alter- 
nately wide  and  narrow,  the  former  reaching  the  inner  wall. 


FIG.  138.  —  Acervularia 
Davidsoni.  VIEW  OF 
A  CLUSTER  OP  CUPS. 


FIG.  139.  —  TRANSVERSE 
SECTION  OF  Acervula- 
ria  Davidsoni.  LARG- 
ER CELLS. 


FIG.  14d.—Lithostrotion  Canadense. 
CARBONIFEROUS  LIMESTONE  OF 
MICHIGAN.  (From  Nature.) 


The  study  of  these  corals  is  very  fascinating;  but  we  have 
pursued  the  subject  quite  far  enough  for  an  elementary  course. 
In  an  advanced  course,  we  shall  resume  the  subject. 


FIGS.  141,  142,  \4£.—Diphyphylhim  Arcfiiaci.  (Billings.)  HAMILTON  GROUP.  (From 
Nature.)  141,  General  View.  142,  Transverse  Section.  Showing  Double  Wall, 
Septa,  Primary  Septum  in  a  Fovea.  143,  Longitudinal  Section.  Showing  Double 
Wall,  Central  Tabnlsp,  and  two  sorts  of  Peripheral  Tissue. 


FURTHER    EXAMINATION    OF    CUP   CORALS.  21? 

From  the  details  enumerated,  let  us  now  gather  together 
definitions  of  the  different  genera  illustrated: 

AMPLEXUS.  Simple,  subcylindrical,  narrowed  toward  the 
lower  extremity,  covered  with  epitheca.  Septa  slender,  very  nar- 
row, equal,  the  chief  septum  in  a  fovea.  Tabulae  horizontal, 
strong,  mostly  complete,  closing  the  bottom  of  the  cup. 

ZAPHRENTIS.  Simple,  horn-shaped  or  top-shaped,  with  epi- 
theca. Cup  deep,  with  a  distinct  fovea.  Septa  well  developed, 
reaching  the  centre,  more  or  less  distinctly  pinnate.  Tabulae  also 
well  developed,  and  reaching  to  the  wall.  In  the  peripheral  region 
sometimes  a  little  coarse  vesicular  tissue. 

STREPTELASMA.  Simple,  conical,  often  curved,  with  epitheca. 
Septa  radiate  in  the  cup,  unequally  broad;  the  broader  set  some- 
what twisted  together  in  the  centre,  and  forming,  with  the  modi- 
fied tabulae,  a  vesicular  eminence.  Chief  septum  and  lateral 
septa  distinctly  shown  externally,  as  also  the  pinnately  arranged 
later  septa.  Tabuing  completely  developed. 

CYATHOPHYLLUM.  Simple  or  compound,  with  epitheca.  Tab- 
ulae in  the  middle  of  the  visceral  cavity,  cellular  tissue  in  the 
peripheral  part.  Septa  numerous,  regularly  radiate,  reaching  the 
centre,  and  sometimes  twisted  there  into  a  feeble  elevation. 

LITHOSTROTIOX.  A  compound  Cyathophyttum,  having  the 
central  vesicular  tissue  condensed  into  a  column  which  rises  in 
the  deep  cup  as  a  solid  striated  cone.  Tubes  striated  externally, 
sometimes  isolated  and  cylindrical. 

HELIOPHYLLUM.  Simple,  top -shaped,  seldom  compound. 
Septa  numerous,  perfectly  developed,  their  sides  decorated  with 
carinae,  or  raised  lines  running  downward  and  inward,  and  arranged 
in  pairs  on  opposite  sides.  Irregular  tabulae  in  the  central  part, 
cellular  tissue  in  the  peripheral.  A  Cyathophyllum,  with  carinae. 

CYSTIPHYLLUM.  Simple  or  compound,  with  epitheca.  Ex- 
terior deeply  wrinkled,  and  the  form  often  elongate,  geniculate, 
or  irregular.  Septa  and  tabulae  extremely  modified,  their  normal 
forms  sometimes  not  appearing,  a  cellular  tissue  filling  the  whole 
visceral  cavity,  the  cells  mostly  somewhat  crescentic  in  form,  and 
generally  arranged  in  distinguishable  laj'ers  from  below  upward. 


218  GEOLOGICAL   STUDIES. 

ACERVULAEIA.  Compound,  stems  sub-parallel,  approximated, 
often  crowded  and  hexagonal.  Cup  with  an  abrupt  pit  in  the 
centre.  Septa  well  developed,  extending  alternately  to  the  centre 
and  to  the  pit.  The  central  part  of  the  visceral  cavity  with  vari- 
ously shaped  tabuke,  the  peripheral  w7ith  cellular  tissue. 

DIPHYPHYLLUM.  Compound,  consisting  of  generally  slen- 
der, cylindrical,  epitheca-covered  cells,  furnished  with  an  interior 
wall  distant  from  the  outer  wall.  Septa  numerous,  reaching  the 
inner  wall.  In  the  interior,  a  series  of  tabulae;  in  the  peripheral 
part,  cellular  tissue. 

EXERCISES. 

Make  some  polished  sections  of  cup  corals.  In  what  respect  are  Strep- 
telasma  and  Zaphrentis  alike?  In  what  respect  unlike?  How  does  Zaph- 
rentis  differ  from  Cyathophyllum?  How  does  Heliophyllum  differ  from  Cy- 
athophyllumf  Copy  Fig.  127  on  a  piece  of  paper,  then  cut  out  the  four 
quadrantal  fascicles,  leaving  them  connected  at  the  centre,  and  fold  them 
together  like  a  half  ball-cover;  do  you  find  an  appearance  like  Fig.  124? 
Copy  Fig.  132.  Copy  Fig.  139.  How  does  Acervularia  differ  from  Diphy- 
pliyllum?  Have  you  been  able  to  identify  any  cup  coral  found  by  yourself? 
Have  you  ever  collected  fossils  except  from  the  Drift?  Do  you  know  any 
locality  at  which  fossils  may  be  obtained  from  the  rocks?  Have  you  ever 
seen  Acervularia  at  Petoskey?  Have  you  polished  any  coral  sections  with 
your  own  hands?  If  so,  let  us  see  them.  To  what  genera  do  they  belong? 
Make  drawings  of  some  of  your  polished  sections  of  cup  corals.  Select  one 
or  two  of  your  most  perfect  specimens  of  cup  corals  and  draw  them. 


STUDY  XXXII.— Examination  of  Some  Tabulate  Corals. 

Our  collection  of  Drift  corals  was  divided,  in  a  former  study, 
into  two  lots.  The  cup  corals,  or  Rugosa,  we  have  now  learned 
how  to  study.  The  other  lot,  or  those  commonly  called  "  petri- 
fied honeycomb,"  we  must  next  take  up  and  examine.  These  are 
quite  as  common  as  the  rugose  corals;  and  it  may  as  well  be 
stated  at  once  that  the  proper  designation  of  the  group  is  TABU- 
LATA,  or  HEXACORALLA.  From  almost  any  neighborhood  within 
the  area  before  denned  we  may  pick  up  specimens  either  identi- 


EXAMINATION  OF  SOME  TABULATE  CORALS. 


219 


cal  with  those  delineated  here,  in  Figs.  144-148,  or  at  least  gen- 
erically  identical  with  them. 

Beginning  with  the  one  represented  by  Fig.   144,  we   see  a 
large  number  of  tube  ends  closely  crowded  together,  and  pressed 


FIGS.  144-148.— VARIOUS  SPECIES  OF  FAVOSITES. 

(From  Nature.) 

144,  F.  favosus  Gf.,  showing  hexagonal  cells,  septal  rudi- 
ments, and  tabulae.  145,  F.  Alpenensis  Win.,  showing 
angular  apertures.  146,  F.  luberosus  Rom.,  showing 
pores.  147,  F.  nitella  Win.,with  cells  small.  148,  F-  clau- 
sus  Rom.,  branched. 

into  hexagonal  forms.     So  far  as  we  can  see, 

any  two  walls  in  contact  are  blended  into  a 

single  common  wall;  but  we  shall  have  to 

examine    more    closely    in    a    thin    section. 

Some  of  the  cells  show  strong  tabulae  crossing  from  side  to  side. 

In  some  the  tabulae  near  the  aperture  have  been  removed,  and  in 

others  no  tabulae  are  in  sight.     But  do  we  discover  any  septa? 

There  are  none  well  characterized;  but  we  plainly  see  a  number 


220 


GEOLOGICAL   STUDIES. 


REPRESENT 

Nature.) 


SEPTA.       (From 


of  point-like  depressions  or  indentations  around   the   border  of 
each  tabula.     Close  inspection  shows  that  these  alternate  with 

small  projections  from  the  inner  walls 
of  the  cells,  and  these  projections  ex- 
tend, as  raised  bands  or  ridges,  length- 
wise of  the  cells.  Fig.  149  is  a  view 
of  another  specimen,  showing  this 
character.  The  raised  bands  or  lines 
are  twelve  in  number,  and  are  sepa- 
rated by  twelve  longitudinal  furrows. 
These  raised  bands  appear  like  the 
stumps  of  septa,  and  the  constancy  of 
^eir  number  confirms  this  interpre- 
WITHIN  THE  CELLS;  THESE  tation. 

If  we  turn  our  attention  to  the  speci- 
men shown  in  Fig.  145  —  Favosites 
Alpenensis,  Winchell  (afterward  described  by  Rominger  as  F. 
Hamiltonensis)  —  we  perceive  that  it  is  part  of  an  elongated, 
rudely  cylindrical,  or  tuberose  mass,  composed  of  small  tubes, 
which  rise  from  a  common  central  axis,  at  a  small  angle, 
and,  after  continuing  a  certain  distance,  curve  toward  the  sur- 
face of  the  mass,  and  present  there  their  terminations  or 
mouths.  These  tubes,  throughout  their  whole  length,  are  crossed 
by  delicate  transverse  plates,  which  can  be  nothing  but  tabulae. 
Hence,  they  are  of  the  same  nature  as  those  seen  in  the  mouths 
of  the  tubes  of  Fig.  144.  Some  of  these  tabulae  extend  quite 
across;  but  some  of  them  join  the  neighboring  ones  above  or 
below,  and  hence  are  incomplete  ;  and  some,  after  touching  their 
neighbors,  continue  separately.  The  tabulae  toward  the  outer 
ends  of  the  tubes  become  quite  crowded.  W^e  notice,  also,  a 
system  of  branching  among  these  tubes.  Many  tubes  do  not 
originate  at  the  centre,  but  start  from  a  point  in  the  wall  between 
two  tubes,  giving  the  wall  an  appearance  as  if  split,  and  thus 
suggesting  that  the  wall  is  really  double.  It  ought  to  be  double, 
if  formed  by  the  union  of  the  two  walls  of  the  two  contiguous 
cells.  This  mode  of  introduction  of  new  cells  is  called  lateral 


EXAMINATION   OF   SOME   TABULATE   CORALS. 


OF  Favosites  Alpe- 
nensis.  SHOWING  < 
TABULA,  LONGI- 
TUDINAL MURAL 
STRIDE,  (but  badly), 
DOUBLE  WALLS,  AND 
LATERAL  BUDDING. 


gemmation,  or  budding  from  the  side.  We  cannot  see  here  the 
longitudinal  bands  and  furrows  which  represent  septa.  Fig.  150, 
however,  is  a  thin  section  of  a  small  globu- 
lar mass  of  this  species.  As  the  tubules  radi- 
ate from  a  centre,  the  section,  in  passing  near 
the  centre,  is  transverse  to  the  central  tubules, 
and  longitudinal  to  those  near  the  exterior. 
Now,  besides  the  conspicuous  tabulae,  we  can 
see  here  the  longitudinal  raised  lines  shown  in 
section,  and  projecting  like  spines  in  the  central 
tubules;  and  we  see,  also,  a  few  pores,  arid  a 
light  line  along  the  middle  of  the  common  wall  FIG.  iso.— THIN  SLICE 
in  the  longitudinal  sections,  proving  plainly 
their  double  character.  [Pores  not  engraved.] 

Now,  if  we  take  the  specimen  represented 
by  Fig.  146,  we  notice,  also,  a  series  of  slightly 
divergent  tubes,  but  with  only  occasional  tab- 
ulae. As  in  some  places  they  stand  close  together,  it  is  proba- 
ble that  most  of  the  tabulae  once  present  have  been  removed. 
We  see  nothing  different  in  the  nature  of  the  walls,  and 
notice  also  the  evidences,  of  lateral  gemmation.  But  there  is 
one  striking  character  not  before  clearly  seen.  The  vertical  walls 
are  perforated  with  numerous  pores  —  also  sparingly  detected  in 
Fig.  150.  These  are  arranged  mostly  in  two  longitudinal  series 
on  each  side,  but  the  number  of  series  depends  on  the  width  of 
the  side.  These  pores  establish  complete 
communication  between  contiguous  cells,  as 
is  shown  in  places  where  the  light  passes 
through. 

Fig.  147  illustrates  a  more  delicate  struc- 
ture, globoid  in  form,  with  small  cells  radi- 
ating   from    a    centre.      But  a  thin   section,   FIG.  151. —THIN  SECTION 
Fig:.  151,  shows  tabulae  and  pores  quite  like      OF    fmositea     mteila. 

mi  X4.    SHOWING  TABULA. 

those  in  the  other  specimens.     1  he  apertures 

of  some  of  the  cells  incline  to  be  round.     There  is  a  type  of 

this  group   having   quite    circular    cell    sections,  and  it  is  very 


222 


GEOLOGICAL   STUDIES. 


abundant  throughout  the  Northwest.  A  group  of  the  cell 
mouths  is  shown  in  Fig.  152.  Here  are  two  sorts  of  mouths. 
First,  larger,  circular  mouths,  about  one 
millimeter  wide,  and  quite  separate 
from  each  other;  second,  small  sub- 
angular  mouths,  about  one-third  the  size 
of  the  others,  standing  close  together, 
and  forming  a  mass  in  which  the  larger 
cells  are  imbedded.  If  we  make  a  ver- 
tical section,  we  shall  see  that  both  the 
large  and  small  cells  are  supplied  with 
tabulae.  We  shall  also  perceive  com- 
municating pores.  But  there  are  no 
FIG.  152.— Favosite*  Canadensis,  longitudinal  grooves,  and  hence  no  indi- 

BILL.   SHOWING  TUBULES  or  catiOns  of  septa.     In  spite  of  the  diver- 
Two  SIZES. 

gences  or  this  type,  we  feel  constrained 

to  unite  it  with  the  other  specimens  having  numerous  tabulae 
and  connecting  pores.  These  all  belong  to  the  great  and  impor- 
«f3Mmr«nvft»«nn  ^ant  genus  known  as  Favosi'tes  (name  from 
favus,  a  honeycomb,  and  the  conventional 
termination  ites). 

A  form  slightly  different  from  any  of  these 
is  also  found  quite  frequently  in  the  Drift  of 
New  York,  Ontario,  and  the  Northwest,  as 
also,  of  course,  in  the  rocks  of  certain  forma- 
tions. This  is  a  rounded,  depressed,  cake-like 
mass,  composed  of  numerous  flattened  tubes 
radiating  from  a  basal  point  (not  seen  in  Figs. 
153.  —  Almontes  153,  154),  reaching  the  surface  at  oblique  an- 
gles, and  opening  in  crescentically  three-angled 
mouths  —  in  other  words,  mouths  like  small  spherical  triangles. 
A  section  parallel  to  the  tube  lengths  shows  the  tube  walls  lon- 
gitudinally grooved  or  striated,  and  perforated  with  large  pores 
situated  on  or  near  the  two  lateral  edges.  It  shows  also  a  series 
of  remote,  irregular  tabulae,  and  also  some  longitudinal  crests 
or  rows  of  spinulose  projections,  which  are  the  homolog-ues  of 


FIG 

Goldfussi,  BILL. 


EXAMINATION  OF  SOME  TABULATE  CORALS. 


223 


FIG.  154. 

SECTION  OF  Alve- 
olites  Goldfussi. 
SHOWING  TABU- 
LAE AND  PORE9. 


septa.     This  is,  therefore,  fundamentally  similar   to  Favosites, 
and  belongs   in  the  same  Family  ;  but,   in  consequence  of  the 
peculiar  form  of  the  tubes  and  tube  mouths,  and 
the  positions  of  the   pores,    it   is   set    down   as    a 
different  genus,  Alveolites  (alveolus,  a  pit,  and  ites, 
as  before). 

Another  form  of  this  family  is  Limaria  (per- 
haps from  limarius,  pertaining  to  slime  or  sedi- 
ment). The  surface  of  a  specimen  is  shown  in 
Fig.  155.  It  looks  much  like  a  small-celled  but 
thick-walled  Favosites.  The  apertures  are  com- 
pressed, and  open  obliquely  to  the  surface.  On  the  outer  side, 
the  lip  bears  two  teeth  projecting  into  the  cavity;  and  on  the 
inner  side  a  single  tooth  projecting 
between  the  two  outer  ones  (Fig.  156). 
A  longitudinal  section  shows  that  the 
tubes  are  connected  by  lateral  pores, 
and  intersected  by  transverse  tabulae. 
The  tabulas  are  mostly  wanting  in  the 
thick-walled  portions  of  the  tubes. 
This  you  perceive  only  differs  from 
Alveolites  in  less  compressed  tubes, 

thicker  walls,  and  fewer  longitudinal  crests.  There  is  another 
genus,  Cladopora  (-/.Xddoq^  a  branch,  and  Kopa,  a  pore,  conven- 
tional name  for  certain  corals),  which  only 
differs  from  Limaria  in  having  no  tooth-like 
projections  in  the  apertures,  and  smooth,  in- 
stead of  crested,  tube  interiors.  Tabulag  exist, 
but  they  are  rarely  seen,  the  tubes  being  gen- 
erally open  from  end  to  end.  Even  longitudi- 
nal furrows,  the  vanishing  indications  of  the 
septal  system,  are  occasionally  seen,  and  are  to 
be  regarded  as  potentially  present.  Lateral 
pores  in  the  walls  are  also  present.  The 
species  shown  in  Fig.  157  is  branching  and  reticulating.  Other 
species,  like  Cladopora  Roemeri,  Fig.  158,  are  simply  branched, 


FIG.  155. 
Limaria  crassa,  ROM. 


FIG. 156. 

MOUTH  AND  TEETH 
OF  Limaria  crassa. 
X  7.  (In  the  spec- 
imen figured  only 
one  tooth  is  seen. 
The  opposite  two 
are  generally  in- 
conspicuous.) 


224 


GEOLOGICAL   STUDIES. 


FIG.  157. 
Cladopora  taqueata,  ROM. 


and   still    others  form   flat,  leaf-like    expansions.      It  would   be 
interesting  to  extend  the  study  of  this  group  of  forms,  but  we 

fear  it  would  occupy  an  undue  pro- 
portion of  the  student's  time.  The  dis- 
tinctive characters  of  this  order  of  fos- 
sils have  been  shown,  as  also  the 
method  of  investigating  them.  It  ap- 
pears that  the  septal  system  is  feebly 
developed,  but  that  the  tabular  system 
is  generally  conspicuous.  For  this 
reason  they  were  named  by  Milne- 
Edwards  TABULATA,  or  Tabulate  Cor- 
als. We  have  seen  also  that  the  furrows  and  ridges  which  rep- 
resent the  septal  system  are  twelve  in  number.  If  we  should 
examine  all  the  genera  of  this  group,  we  would  find  some  with 
six  more  or  less  complete  septa.  So  the  number  in  all  cases  is  a 
multiple  of  six.  As  the  number  among  the  Cup  Corals  is  a  mul- 
tiple of  four,  and  they  have  hence  been  by  Haeckel  styled  TETRA- 
CORALLA,  so  this  Order  has  been  by  the  same  designated  HEXA- 

CORALLA. 

Let  us  now  bring  together  the  characters  of  those  genera 
of  Favositi' dee  which  have  been  illustrated: 
FAVOSITES.  Polypary,  compound,  massive 
(globoid,  tuberose,  pyriform,  or  elongate),  flat- 
tened, or  branching,  composed  of  tubes  which 
are  generally  crowded  and  hexagonal,  but  some- 
times cylindrical,  variable  in  diameter  in  the 
same  species,  and  opening  perpendicularly  to 
the  surface.  Tabulae  generally  numerous  and 
conspicuous,  in  some  species  irregular  or  incom- 
plete. Septa  represented  by  twelve  longitudi- 
nal furrows  and  alternating  ridges,  which  are  in 
some  species  crowned  with  spinules  in  one  or 
more  series.  Walls  perforated  by  pores  in  one, 

two,  or  more  vertical  rows  on   each  side,  but  very  different  in 

number  in  different  species. 


FIG.  158. 

THIN  SLICE  or  Cla- 
dopora Rcemeri, 
BILL.  SHOWING 
THICKENED  DOU- 
BLE WALLS  AND 
DELICATE  Trabec- 
ular  STRUCTURES 
(LIKE  SPIDER 
LINES)  WITHIN 
THE  CELLS.  X  7. 


EXAMINATION    OF   SOME   TABULATE   CORALS.  225 

ALVEOLITES.  Polypary  massive,  convex,  or  flattened,  often 
laminar  or  branched.  Constituent  tubules  flattened  and  closely 
appressed,  opening  obliquely  at  the  surface  with  a  triangular  ori- 
fice bounded  by  three  curved  lines.  Septa  represented  by  longi- 
tudinal furrows.  Tabulae  more  remote  and  irregular  than  in 
FAVOSITES.  Pores  very  large  on  the  two  lateral  edges  of  the 
compressed  tubes. 

LIMARIA.  Small,  branching  stems  or  laminar  expansions, 
composed  of  thick-walled,  conico-cylindrical  tubules,  with  com- 
pressed orifices  opening  obliquely  to  the  surface,  having  a  lip 
bearing  two  tooth-like  projections  on  one  side  and  one  on  the 
opposite.  Septa  feebly  represented  by  three  longitudinal  crests 
on  the  walls.  Tabulae  restricted  to  thinner  portions  of  the  tubules. 
Connecting  pores  present. 

CLADOPOKA.  Ramose,  often  reticulating  sterns  or  laminar 
expansions  —  often  these  different  forms  in  the  same  individual. 
Composed  of  thick-walled,  conical  tubules,  opening  obliquely  to 
the  surface,  and  having  dilated  orifices.  Tubules  laterally  con- 
nected by  pores.  Tabulae  very  rarely  seen.  Longitudinal  fur- 
rows mostly  obsolete,  but  occasionally  discernible. 

EXERCISES. 

Point  out  several  Tabulate  Corals.  Are  they  simple  or  compound  ?  Are 
they  calcareous  or  silicified?  Were  they  obtained  from  the  Drift  or  from 
strata  in  place?  Are  they  nearly  perfect?  Indicate  places  where  defects 
exist.  Are  they  worn  like  Drift  pebbles?  Point  out  some  fracture  which 
passes  between  two  tubules,  if  you  can.  Point  out  some  fracture  which 
passes  through  a  tubule.  Does  this  reveal  the  interior  of  the  tubule?  What 
structures  are  there  revealed?  Point  out  tabulae,  if  present.  Point  out 
longitudinal  furrows  on  the  walls.  What  do  these  represent?  Point  out 
pores,  if  present.  Are  they  scattered  or  numerous?  In  how  many  rows  do 
they  exist  on  each  side?  To  what  genus  does  this  specimen  belong?  Do  the 
mouths  open  vertically  or  obliquely?  What  is  the  form  of  the  tube  section? 
Make  a  drawing  of  a  small  portion  of  the  specimen.  Make  an  enlarged 
drawing  of  two  or  three  tubules,  with  all  the  details.  Pick  out  a  Favosites 
with  cylindrical  tubules.  What  was  'the  form  of  the  specimen  when  entire? 
Explain  how  it  differs  from  the  last  specimen.  How  can  you  most  easily 
detect  Alveolitea  from  external  characters?  Which  two  of  the  four  genera 


226  GEOLOGICAL   STUDIES. 

illustrated  are  least  distinguishable  from  external  characters?    Which  two 
have  thickest  walls? 


STUDY   XXXIII  —  Examination  of  Some  Brachiopods. 

Of  the  numerous  fossils  which  any  person  may  collect  from 
the  Drift,  a  large  proportion  appear  to  be  bivalve  shells — that  is, 
shells  composed  of  two  pieces  intended  to  open  and  close  by  a 
hinge,  like  a  river  mussel.  Among  bivalves,  it  is  extremely  easy 
to  make  a  distinction  based  on  the  external  form  of  the  shell. 
Yet  it  is  a  distinction  of  very  fundamental  value,  since  it  sep- 
arates two  Classes  of  Molluscs. 

To  begin   with,  we  will  take  the  shell  of    a   common  river 

mussel,  Fig.  159, 
the  hinge  side  up. 
The  most  prominent 
part,  «,  is  called  the 
beak.  Now,  any  ob- 
serving boy  has  seen 
the  river  mussel  in 
the  act  of  locomo- 
tion. It  raises  itself 
on  edge,  somewhat 
inclined,  however; 
separates  its  two 

FIG.  159.-LEFT  VALVE  OF  A  COMMON  RIVER  MUSSEL,  UNIO.  valves  sllghtly>  Pro' 
a,  Beak;  h  d,  External  Ligament;  b  c,  Hinge  Border;  (7,  trudes  a  soft  Organ 
Anterior  Border;  A  Posterior  Border;  ,1  5,  Height;  caljed  tfc  j>  f  d 
C  A  Length;  0,  Thickness.  J 

glides  over  the  mud- 
dy bottom  of  the  pond  or  stream,  leaving  a  track  like  the  mark 
of  a  finger.  If  our  shell,  figured  above,  were  in  motion,  it  would 
move  from  right  to  left.  It  appears,  therefore,  that  C  is  the 
anterior  end  and  D  is  the  posterior.  It  appears  that  the  beak  is 
nearest  the  anterior  end,  and  is  turned  in  that  direction.  This 
valve  which  is  figured  is,  therefore,  the  left  valve.  Next,  let  us 
turn  our  mussel  around,  so  as  to  look  at  it  hingewise.  You  notice 


EXAMINATION    OF    SOME    BRACHIOPODS. 


227 


that  the  two  valves  are  equally  convex.  This  is  what  would  be 
expected.  One  is  a  right  valve  and  the  other  a  left;  and  the  law 
of  bilateral,  or  two-sided  symmetry,  which  runs  through  the 
animal  kingdom,  and  applies,  as  we  have  seen,  to  animals  called 
"radiated,"  requires  that  each  shall  be  correspondingly  devel- 
oped. Let  us  call  this  bivalvular  symmetry.  Shells  with  this 
symmetry  are  LAMEL'LIBRANCHS  (Lamella,  and  branchiae,  gills, 
referring  to  the  flat  form  of  the  gills. 


FIG.  160. — A  RIVER  MUSSEL  VIEWED  FROM  THE  HINGE  SIDE,  SHOWING  EQUAL  VALVES. 
This  is  an  extinct  species,  Anodonta  angustata,  from  the  Catskill  Sandstone,  New 
York. 

Now  take  one  of  the  bivalves  picked  up  from  the  Drift. 
There  is  none  more  common  throughout  the  Northwest  than  this 
which  is  here  figured,  and  which  bears  the  name  Spirifera  mu- 
cronata  (spira,  a  spire,  fero,  to 
bear,  and  mucronatus,  pointed, 
the  latter  referring  to  its  extrem- 
ities). Notice  that  the  beak  is 
exactly  in  the  middle  of  the  shell 
between  its  extremities,  and  that 
the  outline  is  symmetrical  around 
the  valve  each  way  from  the 
back.  It  must  be,  then,  that  one  side  of  the  beak  is  the  right 
side,  and  the  other  the  left;  and  if  so,  the  two  valves  are  dorsal 
and  ventral,  instead  of  right  and  left.  Let  us  view  a  shell  from 
the  end,  Fig.  162.  Here  we  immediately  perceive  that  the  two 
valves  are  not  equally  convex,  and  have  not  equally  devel- 
oped beaks.  They  are  not  mutually  symmetrical.  Hence  they 
are  not  right  and  left  valves;  and  we  conclude  as  before,  that 
one  is  dorsal  and  the  other  ventral.  The  law  of  bilateral  sym- 
metry works,  therefore,  separately  in  each  valve,  and  pro- 


FIG.  161.— SPIRIFERA  MUCRONATA,  CON, 
VIEWED  FROM  THE  VENTRAL  SIDE. 
Showing  the  Beak  and  Anterior  Bor- 
der, r,  the  Right  Side ;  I,  the  Left. 


GEOLOGICAL   STUDIES. 


FIG.    162.— SPIRI- 

GEKA  SPlRIFER- 

OIDES.    VIEWED 

FROM   THE  END, 

SHOWING  UNE- 
QUAL VALVES. 
«,  the  So  Called 
Ventral  Valve; 
d,  the  Dorsal. 


duces  what  we  may  call  univalvular  symmetry.  Shells  with 
this  symmetry  are  BRACHIOPODS  (/9^a/c'ww,  arm,  and  TTOUS,  noSoq, 
foot).  The  valve  which  we  will  call  ventral 
always  has  the  most  prominent  beak;  and  it  is 
almost  always  most  convex  or  swollen.  Gener- 
ally, too,  it  has  a  depression  or  sinus  along  the 
middle,  which  corresponds  to  an  elevation  or  fold 
along  the  middle  of  the  dorsal  valve. 

It  is  not  easy  to  determine  which  valve  is 
really  ventral  or  which  dorsal.  Some  of  the  Ger- 
man palaeontologists  say  the  smaller  valve  is  ven- 
tral; while  the  English  say  it  is  the  larger.  The 
only  means  of  deciding  is  an  examination  of  liv- 
ing specimens  belonging  to  this  class.  But  this 
examination  is  not  decisive;  nor  does  it  indicate 
clearly  which  should  be  regarded  the  anterior 
part  and  which  the  posterior.  In  this  state  of  the  case,  the  side 
opposite  the  hinge  is  commonly  regarded  anterior,  though  the 
mouth  was  actually  far  back,  near  the  beak.  In  this  view,  the 
right  side  of  the  shell  will  be  on  the  right  when  the  shell  lies 
on  the  ventral  valve,  with  the  hinge  side  next  the  observer. 
This  is  indicated  in  Fig.  161,  where  the  dorsal  side  is  down. 

These  principles  enable  us  to  draw  important  inferences  from 
small   fragments  of   bivalves.     Suppose  the  line  of    break  of    a 

valve  is  along  a  b,  Fig.  163.  Then, 
the  beak  and  hinge  line  being  present, 
it  appears  that  the  beak  is  central, 
and  the  valve  belonged  to  a  Brachi- 
opod.  If  only  a  part  of  the  hinge  line 
is  preserved,  that  mav  show  symme- 
trical outlines  each  side,  and  thus 
demonstrate  the  same  thing.  If  the 
break  is  along  the  line  c  d,  and  we  have  only  the  small  fragment 
below  that  line,  the  symmetry  in  both  directions  shows  that  the 
break  was  opposite  the  middle,  and  the  shell  was  a  Brachiopod. 
If  the  break  is  along  the  line  e  f,  and  we  have  only  the  small 


FIG.  163.— ORTHIS  BIFORATA, 
VENTRAL  SIDE. 


EXAMINATION    OF    SOME    BRACHIOPODS. 


229 


piece  on  the  right,  if  a  fragment  of  both  valves  is  present,  their 
unequal  convexity  shows  the  shell  a  Brachiopod.  If  we  have 
barely  the  two  beaks  broken  off  at  g  h,  their  unequal  prominence 
declares  a  Brachiopod. 

Now  let  a  Lamellibranch  be  broken  in  the  same  various  ways, 
and  the  style  of  the  symmetry,  or  the  lack  of  symmetry,  will 
show  each  fragment  to  belong  to  a  Lamellibranch.  The  student 
should  practise  mucli  on  these  tests. 

Let  us  give  further  attention  to  these  Brachiopods.  By  col- 
lecting industriously,  we  find  many  with  the  two  valves  separated. 
The  ventral  valve  is  known  by  its 
sinus;  and  this  valve,  you  will  notice, 
bears  a  couple  of  small  processes,  or 
projections,  t,  t,  Fig.  164,  which  are 
called  teeth,  one  on  each  side  of  the 
middle,  on  the  hinge  plate.  These 

are  part  of  the  hinge  structure,  and 

. r                                                     .  FIG.   164.  —  INTERIOR  OF  VENTRAL 

fit    into   two    SOCKetS,   S,  S,   Figs.   165,  VALVE  OF  Spiriferamucronata,t,t. 

166,    in    the    dorsal    valve,     which     is  the  two  teeth;  6,  the  beak;  c,c,  the 


known  by  the  fold.  This  hinge 
structure  is  possessed  by  all  Brachio- 
pods which  have  a  strong  calcareous 
shell.  Between  the  sockets  of  the 
dorsal  valve  is  the  cardinal  process. 


cardinal  extremities ;  a,  the  trans- 
versely striated  area;  /,  the  trian- 
gular fissure,  showing  ledge  for 
reception  of  deltidium;  0,  occlusor 
muscular  scars ;  s,the  median  sinus. 

This  is  a  projection  to 


FIG.  165.— INTERIOR  OP  DORSAL  VALVE 
OF  Spirifera  mucronata.  s,  s,  the 
two  sockets ;  p,  the  cardinal  process 
(here  not  salient) ;  &,  6,  brachial  pro- 
cesses; 0,  occlusor  muscular  scars; 
a,  narrow  area;  /,  the  median  fold. 


FIG.  166.— HINGE  PARTS  OF 
Orthis  subquadrata,  EN- 
LARGED. DORSAL  VALVE. 
s,  s,  sockets;  p,  cardinal 
process,  with  pinnate 
markings;  b,  b,  brachial 
processes.  (Meek.) 


which   is  attached  the  muscle  which  opens  the  two  valves.     In 
some  other  genera  this  is  much  more  developed.     It  is  generally 


230 


GEOLOGICAL   STUDIES. 


Fio.  167.— INTERIOR  OP  DORSAL 
VALVE  OF  Strophome'na  ince- 
quiradiata,  CON.  p,  the  two 
cardinal  or  divaricator  processes. 
0,  the  impressions  of  the  occlu- 
sor  muscles.  (Billings.) 


conspicuous  in    Ort/iis,    as    shown  in    Fig.    166.      In   the   valve 

shown  in  Fig.  167,  Strophome'na 
incequiradiata,  the  cardinal  process 
is  divided,  and  very  strong.  One 
extremity  of  the  divaricator,  or 
opening,  muscle  is  attached  to  this 
process,  and  the  other  to  the  in- 
terior of  the  ventral  valve.  Then, 
contraction  of  the  muscle,  acting  on 
the  cardinal  process,  as  on  the  end  of 
a  lever,  lifts  the  dorsal  valve.  At  the 
place  of  attachment  of  the  divarica- 
tor muscle  is  a  depression,  or  scar, 
on  the  interior  of  the  ventral  valve, 
shown  at  d,  Fig.  168.  There  are  two  muscles  and  two  divaricator 
scars.  The  valves  are  closed  by  two  pairs  of  occlusor  muscles, 

which  pass  directly  across  from  valve 
,o  to  valve,  and  leave  occlusor  scars  on 
the  interior  of  each  valve.  These 
scars  are  shown  at  o,  Figs.  167  and 
168. 

The  hinge  mechanism  is  more 
clearly  shown  in  Fig.  169,  which  rep- 
resents a  section  through  both  valves 
of  a  Strophome'na,  from  hinge  to 

FIG.  168.  —  INTERIOR  or  VENTRAL   front    margin.       The    structures    are 
VALVE  OF  Strophome'na  incequira-         ,.       ,     -,    •       ,1  i         ,•  T,    • 

^  CON.   .,,,  the  sides  ;  m,  the   indicated  in  the  explanation.     It  is 

evident    that    by    the    contraction    of 

*»  x™™^  musc\e  D,  «,«  ^em- 

the  beak,  with  a  narrow  deltidium  ity  of  the  process  jP,  must  be  drawn 
beneath  it;  d,  the  divaricator  fan-  toward  the  point  J)  and  thus  the 
pression,  or  muscular  scar;  0,  the 

occlusor;  t>,  the  vascular  impres-    dorsal  valve  must  turn  on  the  hinge 

sions;  r,  the  teeth.  at  ^  ag   ft    door   tums   Qn   jtg   hinges. 

By  this  movement  the  valves  were  separated  at  the  front  mar- 
gin, M.  By  the  contraction  of  the  occlusor,  O,  the  valves  were 
drawn  together. 


f  ront  margin  ;  c,c,  the  cardinal  an- 


EXAMINATION    OF   SOME   BRACHIOPODS. 


231 


VALVES  FROM  BEAK  TO  FRONT,  THE  UPPER 
VALVE  THE  DORSAL.  J/,  the  front  margm ;  A, 
area  of  ventral  valve ;  S,  socket  in  dorsal  valve 
for  reception  of  tooth  of  ventral  valve;  P,  di- 
varicator,  or  cardinal,  process  (or  lever);  7>, 
divaricator  muscle;  0,  occlusor,  or  adductor. 
(After  Billings.) 


Referring  again  to  the  ventral  or  toothed  valve  of  Spirifera 
mucronata,  Fig.  164,  we  no- 
tice, further,  the  flat  elon- 
gate-triangular space  a,  un- 
der the  beak  b,  and  extend- 
ing the  whole  length  of  the 
hinge  line.  This  is  the  area' 

and    most   Brachiopods    pos-    FlG-  169.— DIAGRAM  or  THE  HINGE  MECHANISM 

,  ,        OP  A  BRACHIOPOD.    SECTION  THROUGH  BOTH 

sess    it   only   in   the   ventral 

valve,  though  some  are  des- 
titute of  it,  and  some  have 
an  area  in  each  valve.      No- 
tice the  notch  or  fissure  in 
the     margin     of     the     area. 
There  is  a  delicate  ledge  on  the  two  sides,  on  which,  in  the  per- 
fect state,  rests  a  cover,  like  a  stove  lid,  called  deltidium,  in  allu- 
sion to  its  deltoid  shape.     It  consists  of  two 
pieces,  a  right  and  left.     Sometimes  the  ros- 
tral portion  (nearest  the  beak)  of  the  fissure, 
or  even  the  whole  of  it,  becomes  covered  by 
an  arched  pseudodeltidium  fixed  in  position. 
This    is    shown  in    Cyrti'na   Hamiltonensis, 
Fig.  170.     But  here  the  hinge  portion  of  the 
fissure  is  covered. 

Besides  the  muscular  scars  which  may  be 
seen  in  the  interior  of  all  Brachiopods,  there 
are  always  vascular  impressions  correspond- 
ing to  the  positions  of  the  vessels  and  struc- 
tures of  the  internal  parts.  These  are  shown 
in  Figs.  167  and  168.  In  Fig.  171  we  have 
the  interior  of  a  ventral  valve,  showing  va- 
rious structures,  and  the  student  may  exer- 
cise himself  in  pointing  out  and  naming 
them. 

Referring  once  more  to  the  dorsal  valve  of 
Spirifera  mucronata.  Fig.  165,  we  see  two  projections,  b,  b, 


PS 


FIG.  170.—  Cyrtina 
Hamiltonensis .  DOR- 
SAL SIDE  OF  A  LARGE 
SPECIMEN.  6,  the  very 
prominent  ventral 
beak ;  a,  the  area ;  ps, 
pseudodelt  idium, 
broken  away  near  the 
beak ;  /,  fold  of  dor- 
sal valve,  on  each  side 
of  which  are  the  ra- 
dial plications,  or 
ribs;  and  these  are 
crossed,  especially 
near  the  margin,  by 
concentric  lines  of 
growth. 


232 


GEOLOGICAL    STUDIES. 


called  brachial  processes,  the  uses  of  which  we  must  inquire 
into.  In  getting  together  a  considerable  number  of  speci- 
mens with  the  two  valves  in  place,  it  sometimes  happens  that  one 
of  the  valves  is  broken  away,  or  weathered  away,  so  as  to  reveal 

some  internal  hard 
structures.  It  is 
not  a  very  extraor- 
dinary thing  to  find 
a  specimen  expos- 
ing an  internal 


FIG.  171.— 
rata.  INTERIOR  OP  VEN- 
TRAL VALVE,  SHOWING 
MUSCULAR  IMPRES- 
SIONS, HINGE  TEETH, 
AND  VASCULAR  MARK- 
INGS. (Meek.) 


spre, 


as  shown  in 


FIG.  n2.—Spirifera  mucrona- 

ta,  WITH   DORSAL  VALVE  T-,  •          i  rvo 

PICKED    AWAY    TO    EXPOSE  Fl^     173>     th°U£h 

THE  SPIRES.    (From  Nature.)  not    SO     completely 

The  Dental  Sockets  and  other  ag  fa  Th 

parts  may  also  be  seen;  but 

the   spires  cannot  be  traced  shell  has  here  been 

completely  to   the    Brachial  carefully    picked 
Processes.  J     r 

away;  and  this  any 

student  can  do  for  himself  by  using  a  knife  point,  or  other  stout  steel 
implement.  These  spires  cannot  be  traced  completely  to  connec- 
tion with  the  brachial  processes,  but  they  can  be  seen  approach- 
ing them.  These  processes,  shown  at  b,  Fig.  165,  are  evidently 
the  real  points  of  attachment  of  the  spires  to  the  shell.  The 
spires  are  arm  supports  for  the  spiral, 
fleshy,  fringed  arms  which  existed  in  the 
living  state,  and  they  are,  hence,  some- 
times styled  the  armature.  The  two  spires 
are  generally  connected  together  by  a  band 
(Fig.  173).  This,  in  some  genera,  is  sim- 
ple, and  nearly  direct,  as  here  shown,  and 
in  other  genera  becomes  remarkably  modi- 
fied. 

It  is  natural  to  wonder  how  the  student 
can  know  that  a  spire  exists  within  a  shell, 
since  there  are  many  Brachiopods  which 

have  no  calcareous    spires  —  some  even  which   resemble   in    ex- 
ternal form  the  most  common  of  those  which  have  spires.     For 


FIG.  173.—  Spirlfera  stri- 
ata,  Sow,  WITH  THE  VEN- 
TRAL VALVE  BROKEN 
AWAY,  SHOWING  THE 
Two  SPIRES  AND  THE 
SIMPLE  CONNECTING 
BAND.  (Woodward.) 


EXAMINATION    OF    SOME    BRACHIOPODS.  233 

instance,  a  striking  general  resemblance  exists  between  Orthis 
bif'ora'ta,  Fig.  163,  and  Spirif' era  mucronata,  Fig.  161.  The 
former,  on  account  of  its  form,  was  long  called  Spirifera  bi- 
forata,  until  it  was  proved  to  have  no  spires,  but  on  the  contrary, 
to  possess  the  peculiar  muscular  scars  which  characterize  Orthis. 
Now,  we  need  not  wait  to  discover  specimens  naturally 
broken  or  worn  so  as  to  reveal  the  interior.  Sometimes  with 
a  pointed  tool  we  may  pick  away  the  shell  sufficiently  to  re- 
veal the  existence  or  non-existence  of  a  spire.  In  any  case,  we 
can  grind  down  one  of  the  valves  by  the  means  explained  in  Study 
XXX.  When  we  reach  the  region  of  the  spires,  each  turn  will 
l>e  ground  off,  and  they  will  be  shown  on  the  ground  surface  by 
clear  points  symmetrically  arranged  as 
illustrated  in  Fig.  174,  where  the  places 
of  the  cut  spire  turns  are  seen  at  s,  s. 
It  is  evident  that  by  continuing  to  grind, 
every  structure  in  the  shell  will  be  suc- 
cessively intersected.  If,  therefore,  we 

make  frequent  examinations  as  we  pro-      *I/^- 

GROUND  DOWN  FROM  BOTH 

ceed,  and  mark  down  in  a  succession  of         SIDES,   s,  .?,  sections  of  the 

drawings,  the  positions  of  the  sections         ^  '  whorls-   (From   Na' 

of  each  structure,  we  shall  have,  in  the 

end,  the  means  of  producing  a  connected  delineation  of  the  whole 

interior. 

The  complicated  armature  of  the  little  Brachiopod  known  as 
Centronella  Julia,  Fig.  187,  188,  189,  was  worked  out  by  break- 
ing in  the  pincers  a  large  number  of  specimens,  in  various  longi- 
tudinal and  transverse  positions,  and  marking  down  each  time 
the  places  of  the  various  structures  broken  through. 

In  other  cases,  where  the  substance  of  the  shell  and  its  filling 
is  somewhat  crystalline  and  translucent,  we  may  grind  off  all 
parts  of  the  exterior  until  the  light  shines  through.  Then,  hold- 
ing the  specimen  between  the  eye  and  a  window,  the  internal 
structures  are  revealed.  It  was  by  such  means  that  the  internal 
spires  were  discovered  in  the  little  shell  known  as  Zygospira 
modesta,  Fig.  178. 


234  GEOLOGICAL   STUDIES. 

EXERCISES. 

Take  a  Lamellibranch  shell  and  point  out  anterior  end.  The  right  valve. 
Take  a  Brachiopod  and  indicate  the  ventral  valve.  What  are  the  external 
indications  of  the  ventral  valve?  What  the  external  indications  of  dorsal 
valve?  Take  various  fragments  of  Brachiopods  and  explain  what  characters 
show  them  to  be  such.  Show  areas  in  specimens  at  hand.  Show  place  of 
deltidium.  Can  you  find  any  pseudodeltidium  ?  Enumerate  all  the  charac- 
ters which  can  be  seen  with  the  valves  closed.  Enumerate  structures  con- 
cealed by  the  closed  valves.  Take  a  separated  valve  and  show  the  hinge 
plate.  Does  it  bear  an  area?  Has  it  sinus  or  fold?  Is  it  dorsal  or  ventral? 
If  dorsal,  point  out  the  cardinal  process.  Point  out  the  hinge  sockets. 
Point  out  the  brachial  processes.  Point  out  occlusor  scars  and  any  other 
characters.  If  it  is  ventral,  indicate  the  teeth.  Show  the  divaricator  scars. 
To  which  valve  are  the  arms  attached?  Construct  a  model,  if  you  can, 
showing  the  mechanism  of  the  hinge  action  of  a  Brachiopod;  make  the 
valves  of  wood,  and  for  muscles  use  pieces  of  India  rubber  bands.  Take 
some  specimens  and  investigate  them  in  the  various  ways  described,  and  see 
what  internal  structures  can  be  discovered,  and  report  results  at  next  study. 


STUDY  XXXIV.—  Further  Examination  of  jBrachiopods. 

The  two  spire-bearing  specimens  examined  (Figs.  172  and  173) 
show  the  spires  lying  with  their  apices  turned  outward.  The 
study  of  other  specimens  would  show  the  spires  generally  in  the 
same  position.  One  of  the  commonest  fossils  of  the  northwest, 
however,  A'trypa  reticularis,  has  the  apices  of  the  spires  turned 
toward  the  centre  of  the  dorsal  valve.  This 
is  well  shown  in  Fig.  175,  where  we  see,  also, 
a  plain  connecting  band  lying  in  the  hinge 
region,  and  having  its  middle  part  bent  for- 
ward. This  species  is  thin  and  elegant 
when  young;  but  with  age  it  grows  plump 
and  finally  very  obese.  Different  individu- 

FIG  175  —Atrypa  reticu-      a^s  a^so  Differ  in  smoothness  and  form.    Con- 
laris,  LINN.   sp.  WITH      sequently,  inexperienced    collectors,  having 


SHOWING  THE   APICES  specimens,  feel  some  disappointment  in  be- 

er THE  SPIRES.  &  con-  ing  told    they    all    belong   to    one    species. 

necting   band.     (After  .                           *                           fe 

Whitfieid.)  Figs.  176  and  177  are  views  of  exteriors. 


FURTHER    EXAMINATION    OF    BRACHIOPODS. 


235 


In  the  southern  part  of  Ohio  and  Indiana  is  found  in  great 
abundance,  an  elegant  little  shell  now  known  as  Zygospira  mod- 
esta,  Conrad  sp.  (Fig.  178).  Thousands  of  them  have  been 
picked  up  at  Cincinnati;  but  they  are  also  widely  dispersed 
through  the  Northwest.  Here  you  see  very  loose  spires  having 
their  apices  turned  nearly  toward  the  centre  of  the  dorsal  valve, 
as  in  A!  try  pa.  They  are  also  connected  by  a  simple  band; 
but  it  arises  from  the  first  turns  of  the  spires,  after  they  have 
reached  the  anterior  part  of  the  shell. 


FIGS.  176,  \Tl.-Atrypa,  reticularis,  EXTERIORS.  176,  Dorsal  side  of  thin  specimen.  177, 
Hinge  margin  of  an  obese  specimen. 

FIG.  178.  —  Zygospira  modesta.  ENLARGED  ABOUT  Six  DIAMETERS.  MOST  OF  THE  VEN- 
TRAL VALVE  is  BROKEN  AWAY  TO  SHOW  THE  INTERNAL  SPIRES. 

Probably,  in  our  collection  of  fossil  Brachiopods,  is  a  speci- 
men like  Figs.  179  and  162,  since  this  species  is  quite  common. 
It  has  a  circular  perforation  in  apex  of  the  ven- 
tral beak.  The  outline  is  sub-oval,  both  valves 
are  rather  convex,  and  the  surface  is  marked  by 
concentric  wrinkles  or  lines  of  growth.  It  is 
known  as  Spiriy'era  spiriferoi'cles,  and  also  as 
Ath'yris  spiriferoi'des.  It  is  a  common  thing 
to  find  one  of  the  valves  broken  or  worn  so  as 
to  expose  the  internal  spires.  It  is  only  a  few 
years  since  Professor  James  Hall  succeeded  for 
the  first  time  in  showing  the  complicated  char- 
acter of  the  connecting  band  in  this  genus. 
Some  conception  of  it  may  be  formed  from 
Fig.  180.  Suppose  we  take  the  specimen, 
Fig.  179,  and  lay  it  on  the  dorsal  side,  with  the 
beaks  to  the  right.  Then  conceive  both  valves 


FIG.  Yft.—  Spirigf- 
era  spirtftr  aides, 
Hall.  VIEW  FROM 
THE  DORSAL  SIDE. 
a,  beak  of  ventral 
valve  with  circu- 
lar perforation. 
For  edge  view 
showing  commis- 
sure, see  Fig.  162. 


236 


GEOLOGICAL    STUDIES. 


taken  away  and  the  spires  left  lying.  Then  imagine  the  whole 
of  both  spires  removed,  except  their  first  (basal  or  central)  turns, 

and  their  connections  with  the 
brachial  plates  at  rt,  and  also 
the  complicated  connecting 
band.  What  remains,  enlarged 
about  four  times,  is  the  part 
shown  in  Fig.  180.  Consider 
the  nearest,  or  left  hand  spire. 
It  is  indicated  by  the  shading. 

FIG.   180.- CENTRAL  PORTION   or  ARMA-       It  starts  at  «,  from  the  brachial 
TURE   OP  Spirig'era  spiriferoides.    The 
lower  side  of  the  figure  is  the  dorsal  side.        process,  extends  torward  a  short 

distance,    then     turns    upward 

and  backward  as  shown  at  6,  and  diverging  somewhat  toward  the 
left  margin,  passes  down  into  the  dorsal  valve,  and  begins  the 
first  or  basal  turn  of  the  spire.  At  i  it  is  represented  as  broken 
oil.  The  connecting  band  springs  up  at  d,  as  a  flattened  process 
which  twists  around  so  that  the  outside  becomes  inside  and  joins 
its  fellow  from  the  other  side  at  e  ;  then  the  two  turn  straight 
backward,  make  a  right  angle  upward  toward  the  ventral  valve, 
and,  separating  at/',  the  left  hand  branch  describes  a  backward 

curve  to  //,  and  then  bends 
downward  nearly  parallel 
with  the  first  turn  of  the 
spire,  and  forward  to  A, 
where  it  joins  the  spire. 


PIG.  \8\..—Syringoth'yris  typus,  Win.  Z>,  Dorsal 
valve.  7,  Ventral  valve.  I,  I,  Dental  lamelhe. 
A  B,  line  of  section  shown  in  Fig.  182.  The  high 
beak  is  turned  down. 


FIG.  182.— PECULIAR  INTERNAL 
STRUCTURE  OP  Syringoth'yris 
typus,  Win.  Section  along  the 
line  A  B  in  Fig.  181.  /,  I,  dental 
lamellae ;  mm,  transverse  plate ; 
<,  fissured  tube. 


FURTHER  EXAMINATION"  OF  BRACHIOPODS. 


237 


FIG.  183.— INTERNAL  STRUCTURE  of 
Syringoth'yris  distans,  Sow.  (Zittel.) 
From  the  Carboniferous  Limestone 
of  Belgium.  D,  pseudodeltidium; 
a;,  dental  lamellae;  y,  transverse 
plate;  z,  fissured  tube. 


Various  other  modifications  of  the  connecting  band  exist  in  other 
genera. 

In  central  and  northern  Ohio,  and  in  Iowa  and  Michigan,  is 
another  peculiar  modification  of  the  internal  structure  of  spire- 
bearing  shells,  which  has  been 
named  Syrlngoth'yris.  The  com- 
monest species  is  S.  typus,  Win- 
chell.  It  has,  as  Fig.  181  shows,  a 
very  high  beak  in  the  ventral  valve, 
and  an  enormous  triangular  area, 
with  a  three-cornered  opening 
sometimes  partially  closed  by  a 
pseudodeltidiurn,  D,  Fig.  183. 
From  the  dental  lamellce,  Z,  I, 
Fig.  182,  springs,  on  each  side,  a 
transverse  plate,  m  m,  and  these 
meeting  in  the  median  plane 
curve  downward  and  are  so  bent  as  to  form  the  two  sides  of  a 
fissured  tube,  t.  Fig.  183  illustrates  the  modification  of  this  struc- 
ture in  a  European  species  of 
the  same  genus. 

All  the  Brachiopods  thus  far 
illustrated  are  spire-bearing, 
and  constitute,  with  still  other 
genera,  the  family  Spirifer' idee. 
How  they  are  to  be  studied  has 
been  shown  with  sufficient  de- 
tail for  a  student  of  the  ele- 
ments of  geology.  But  I  must 
not  leave  the  impression  that  all 
Brachiopods  are  spire-bearing. 
The  highest  family,  Terebratu'- 
lidce,  is  composed  of  genera 
which  have  a  loop.  This  pre- 
sents many  curious  modifications,  but  as  most  of  the  species 
belong  to  formations  and  ages  (Mesozoic)  not  represented  in 


FIGS.  184, 185.  Ter- 
ebratula  Romin- 
gei'i,  WIN.,  HAM- 
ILTON GROUP: 
MICHIGAN,  NAT. 
SIZE.  184— View 
from  dorsal  side, 
with  most  of  dor- 
sal valve  removed, 
showing  short 
loop,  I;  &',  beak 
of  dorsal  valve; 
d\  deltidium. 


185  — VIEW  FROM 
LATERAL  COMMIS- 
SURE, SHOWING 
THE  LOOP  TKOM 
THE  SIDE,  a,  an- 
terior margin;  b, 
beak  of  ventral 
valve  with  circu- 
lar perforation ; 
cJ,  dorsal  valve ; 
»,  ventral  valve; 
J,  loop. 


238 


GEOLOGICAL    STUDIES. 


the  rocks  occurring  near  the  homes  of  most  who  use  this  book, 
I  shall  offer  only  two  illustrations.  The  first  is  Terebrat'ula. 
The  form  of  the  shell  is  ovoid  —  very  different  from  most  of  the 
spire  bearers;  the  hinge  line  is  short,  Fig.  184,  and  the  ven- 
tral beak  has  a  circular  perforation.  The  exterior  is  nearly 
smooth  and  marked  by  a  few  concentric  striations,  or  it  is 
radially  striated  and  rarely  plicated.  Examined  with  a  lens,  it 
is  seen  marked  by  thousands  of  minute  punctations,  like  needle 
pricks,  and  this  is  true  of  the  whole  family.  The  armature 
consists  of  a  loop,  which  extends  from  the  brachial  processes 
forward,  and  is  generally  turned  back  into  the  ventral  valve 
at  the  anterior  extremity.  This  is  shown  in  Figs.  184,  185, 


b> 


189 

FIGS.  187,  188,  189  —  Centronella  Julia,  WAVERLT  OR 
MARSHALL  GROUP.  187.  View  from  dorsal  side, 
X3.  188.  Dorsal  view  of  loop,  X4.  189.  Lateral 
view  of  loop  and  vertical  plate,  X4. 

and  more  in  detail  in  Fig.  186. 

The  only  other  genus  to  which  I 
shall  refer  is  Centronella.  The  loop 
has  been  fully  worked  out  in  the  spe- 
cies Centronella  Julia,  which  is  illus- 
trated in  Figs.  187, 188, 189.  The  loop 
is  shown  in  Figs.  188,  189.  The  geo- 
logical position  is  possibly  in  the  Che- 
mung. 

Many  of  the  Brachiopods  found  in 
the  Drift  are  entirely  destitute  of  cal- 
careous armature,  either  spire  or  loop. 
An  extremely  common  form  is  somewhat  semicircular  in  outline, 


FIG.  186—  LOOP  OP  Terebrat'ula 
(Waldheim'ia)  flavescens.  Re- 
cent. [The  name  of  a  sub-ge- 
nus stands  in  parenthesis  after 
the  name  of  the  genus.]  c  c, 
cardinal  process;  s,  dental 
sockets,  connected  by  hinge- 

•  plate ;  /,  loop,  the  anterior  por- 
tion of  which  is  seen  reflected; 
a,  a,  anterior  and  posterior  ad- 
ductor or  occlueor  scars  (each 
in  pair),  with  the  median  sep- 
tum between.  This  sub-genus 
of  Terebratula  has  a  large  and 
reflected  loop.  Compare  Figs. 
184,  185. 


FURTHER    EXAMINATION    OF    BRACHIOPODS. 


239 


having  the  ventral  valve  very  convex  and  the  dorsal  concave. 
Some  of  these  forms  were  figured  for  the  purpose  of  showing 
hinge  structures  and  other  internal  characters.  (See  Figs. 
167,  168,  169.)  Here,  in  Fig.  190,  is  given  a  view  of  the  ven- 
tral valve  of  Strophome'na  inceqruiradiata,  Con.  Fig.  191 
shows  the  dorsal  valve  of  /Strophome'na  alternata,  Con.,  as 
also  the  area  and  depressed  beak  of  the  ventral  valve,  and  the 
arched  pseudodeltidium.  The  dorsal  valve  of  Strophomena  is 


FIG.   190  -  Strophome'na  in- 
cequiradiata,  DEVONIAN. 

View    from    ventral    side.  FIG.   191- Strophome'na  alternate   CAM- 
(Billings.)  BRIAN.      Dorsal    view,    showing    also 

area   and   pseudodeltidium  of   ventral 

valve.    (Meek.) 


FIG.  192— LONGI- 
TUDINAL SEC- 
TION THROUGH 

THE         TWO 

VALVES  OP  S. 
incequiradi- 
ata.  (Billings.) 


externally  concave,  as  is  shown  by  the  longitudinal  section, 
Fig.  192. 

The  further  study  of  Brachiopods  belongs  in  an  advanced 
course.  The  descriptions  and  illustrations  of  internal  structures 
already  given  are  far  more  than  is  customary  in  elementary  trea- 
tises; but  they  have  been  given  because  the  illustrative  speci- 
mens can  nearly  all  be  picked  up  from  the  Drift,  and  worked  out 
by  the  student.  They  belong  to  the  accessible  inductive  data  of 
the  science;  and  because  the  student  can  reach  them  by  his  own 
manipulation  and  research,  I  am  sure  they  will  awaken  an  eager 
interest. 

The  student  making  actual  researches  will   be  aided  by  the 


240  GEOLOGICAL   STUDIES. 

following  table,  in  which  the  characters  pertaining  to  each  valve 
are  brought  together  by  themselves  : 

VENTRAL  VALVE.  DORSAL  VALVE. 

EXTERNAL  CHARACTERS.  EXTERNAL  CHARACTERS. 

Most  prominent  Beak. 
Perforation  for  pedicle,  if  any. 

Most  conspicuous  Area.  Area  generally  wanting. 

Notch  or  Fissure  in  Area.  Notch  present  when  area  is. 

Deltidium  or  False  Deltidium. 

Sinus,   if   one   exists   (save    in   very  few       Fold,   if   one    exists    (sinus   in  very   few 
forms).  forms). 

INTERNAL  CHARACTERS.  INTERNAL  CHARACTERS. 

Teeth  for  articulation.  Sockets,  to  receive  teeth  of  opposite  valve. 

Divaricator  Scars  (generally  one  large  one        Cardinal  Process  (for  attachment  of  Di- 

each  side  of  median  line).  varicator  muscles). 

Occlusor  Scars  (generally  two  crowded  be-       Occlusor  Scars  (generally  four). 

tween  the  rear  parts  of  the  Divaricators). 

Dental  Lamellae.  Foveal  Plates  bearing  the  Sockets. 

Armature  (Spires  or  Loop). 
Crtira  (or  basal  portions  of  Armature). 
Brachial  Process  (for  attachment  of  Arma- 
ture). 

Finally,  to  aid  the  real  working  student,  I  append  an  ana- 
lytical table,  but  only  of  the  genera  here  illustrated,  most  of 
which  are  by  far  the  commonest,  whether  in  the  Drift  or  in  the 
rocks.  Two  or  three  genera  are  here  included,  because  they  pos- 
sess interesting  internal  characters.  The  table  is  based  on  the 
method  which  the  young  student  will  naturally  pursue  —  first, 
observation  of  external  form  and  other  characters;  then,  study 
of  internal  characters  : 

TABLE  FOR  DETERMINATION  OF  SOME  COMMON  BRACHIOPODS. 

Hinge  line  long  and  straight ;  often  the  greatest  transverse  diameter  of  the 
shell.  Form  of  shell  somewhat  triangular  or  semicircular. 
Beak  im perforate.  Surface  plicated  or  striated. 

Sinus  and  fold  well  developed.  Form  more  or  less  angulated  at  the  hinge 
extremities;  sometimes  rounded.  Exterior  distinctly,  often 
strongly,  plicated. 

.  Area  only  in  ventral  valve,  which  has  a  triangular  notch.  Armature  con- 
sisting of  two  spires  having  the  apices  turned  to  the  right  and 
left. 


FURTHER    EXAMINATION    OF    BRACHIOPODS.  241 

No  pseudodeltidiurn. 

SPIRIFEBA.     Figs.  161,  162,  164,  165,  172,  173,  174. 
Pseudodeltidiuin  present.     Ventral  beak  very  prominent;   area  very 

large. 

Exterior  sharply  plicated.    Pseudodeltidium  complete.     Shell  struc- 
ture punctate. 
CYRTINA.     Fig.  170. 

Exterior  with  medium-sized,  rounded  plications.  Pseudodeltidium 
partial.  Notch  with  a  deep  transverse  plate,  beneath  which  is 
a  fissured  tube. 

SYRINGOTHYRIS.     Figs.  181,  182,  183. 

Area  in  each  valve,  nearly  equal  in  the  two.     Triangular  notch  in  each 
valve.     No  calcareous  armature.     Saucer-like  pits  within  for 
insertion  of  muscles;  exterior  sharply  plicated. 
Delthyroid  Section  of  ORTHIS.     Figs.  163,  166. 

Sinus  and  fold  wanting  or  feebly  developed.  Outline  somewhat  semi- 
circular. Area  in  each  valve,  the  ventral  the  broadest,  and 
having  a  triangular  notch,  which  is  sometimes  covered  by  a 
pseudodeltidium.  Ventral  valve  very  convex ;  the  dorsal  often 
concave  externally.  Surface  radiately  striated.  Cardinal  proc- 
ess bifid  and  prominent.  Calcareous  armature  wanting. 
Non-resupiriate  Section  of  STROPHOMENA.  Figs.  167,  168,  172, 
191,  192.  [The  "  resupinate  "  section  has  the  ventral  valve  con- 
cave, and  dorsal  convex.] 

Hinge  line  short,  generally  inconspicuous.     Exterior  plicated,  concentrically 

wrinkled,  or  smooth.     Perforation  at  or  beneath  the  ventral 

beak,   either  conspicuous  or  half -concealed.     Sinus  and  fold 

wanting  or  indistinct.     Form  ovoid. 

Area   beneath   ventral  beak,  and  having  a  triangular  notch.     Spires 

within. 

Rostral  perforation  conspicuous.     Exterior  concentrically  wrinkled. 
Sinus  and  fold  nearly  absent.     Apices  of  spires  turned  outward. 
SPIRIGERA.     Figs.  179,  180. 
Rostral   perforation  concealed   or   inconspicuous.     Apices   of  spires 

turned  toward  centre  of  dorsal  valve. 

Exterior  with  strong,  sometimes  squamous  or  even  spiny,  concentric 
markings,  and  strong  radial  plications.     Adult   shell   tumid. 
Coils  of  spires  numerous  and  crowded. 
ATRYPA.     Figs.  175,  176,  177. 

Exterior  without  conspicuous  concentric  markings:  radial  plications 
small.  Adult  shell  small  and  lean.  Whorls  of  spires  few  and 
loose. 


242  GEOLOGICAL   STUDIES. 

ZYGOSPIRA.     Fig.  178. 

Area  beneath  ventral  beak  wanting  or  scarcely  perceptible.  Notch  usu- 
ally opening  into  the  large,  circular  rostral  perforation,  and 
generally  closed  by  a  pair  of  deltidial  pieces.  Exterior  smooth 
or  concentrically  lined,  or  radially  striate  or  plicate.  Sinus  and 
fold  sometimes  wanting,  generally  little  developed,  and  some- 
times both  valves  feebly  sinuate  near  anterior  margin.  Shell 
minutely  punctate.  Armature  a  loop. 
The  loop  anteriorly  folded  back;  not  embracing  a  free,  vertical  plate. 

TEREBRATULA.     Figs.  184,  185,  186. 

The  loop  not  folded  back  anteriorly,  embracing  a  vertical,  free,  longi- 
tudinal, spiny-margined  plate. 
CENTRONELLA.     Figs.  187,  188,  189. 

EXERCISES. 

What  results  have  you  reached  in  the  investigations  proposed  at  the  last 
study?  Test  the  "Table  for  Determinations"  with  all  the  Brachiopods  you 
get.  Try  to  make  a  model  of  the  armature  of  Spirigera,  using  cork,  paste- 
board, and  mucilage.  Make  a  model  of  the  armature  of  Centronella.  Make 
a  model  of  the  armature  of  Terebratula  flavescens.  Make  a  model  of  the 
hinge  region  of  Syringothyris,  using  white  pine,  pasteboard,  and  mucilage. 
Copy,  with  lead  pencil  or  with  India  ink,  any  of  the  illustrations  of  Brachi- 
opods. Make  a  drawing  of  a  Brachiopod  collected  by  yourself.  Grind  down 
a  specimen  so  as  to  demonstrate  the  nature  of  its  armature.  Show  a  speci- 
men having  a  pseudodeltidium.  Pick  out  all  the  specimens  differing  from 
any  of  the  genera  here  described.  Take  one  of  these  and  write  out  a  descrip- 
tion for  yourself,  first  using  the  external  characters.  Make  a  drawing  of  the 
same.  Find  out  all  possible  of  the  internal  characters.  Write  a  description 
of  them.  Which  of  the  genera  here  described  does  this  specimen  most 
resemble?  What  prevents  its  belonging  to  that  genus?  Take  another  speci- 
men different  from  any  genus  here  described,  and  state  whether  you  think  it 
has  any  calcareous  armature.  If  it  has,  do  you  think  it  a  pair  of  spires? 
Have  you  ever  noticed  a  resupinate  species?  What  genera  have  an  area  in 
each  valve? 


We  have  now  pursued  this  method  of  instruction  as  far  as  the 
time  of  the  elementary  student  will  permit.  We  have  shown  him 
how  to  take  his  lesson  from  nature,  and  have  inspired,  it  is  hoped, 
some  enthusiasm  for  the  science.  He  has  collected;  he  has  ob- 
served; he  has  drawn  inferences;  and  from  these  he  has  reasoned 


FURTHER   EXAMINATION    OF   BRACIIIOPODS.  243 

out  other  facts  which  could  not  be  observed.  This  is  the  method 
by  which  investigators  have  created  the  science.  It  is  the  natural 
method  of  beginning  the  study.  The  method  might  very  advan- 
tageously be  extended  over  various  departments  of  the  field  not 
yet  mentioned;  but  our  time  is  insufficient. 

The  facts  and  conclusions  reached  thus  far  must  necessarily 
exist  for  the  present  in  a  partially  undigested,  confused,  and  un- 
satisfactory state.  The  scattered  facts  and  principles  reached  by 
the  observational  and  inductive  method  which  we  have  pursued 
ought  now  to  be  reviewed  under  some  systematic  and  logical 
arrangement.  A  good  amount  has  already  been  done  in  the 
course  of  these  Studies,  to  bring  facts  into  systematic  arrange- 
ment; but  it  would  be  well  if  the  student  could  now  review  the 
whole  body  of  facts  in  logical  order.  As  this,  with  most  students, 
would  require  more  time  than  can  be  afforded,  we  are  forced  to 
reduce  Part  II  chiefly  to  a  statement  of  some  broader  generaliza- 
tions than  have  yet  been  made,  and  the  presentation  of  some 
important  additional  facts  and  principles  which  cannot  be  omitted 
from  the  elements  of  the  science. 


PART  II. 


SYSTEMATIC   STUDIES; 


OR,   OUTLINES    OF  A    LOGICAL    ARRANGEMENT    OF    THE    FACTS    AND 
THE    LESSONS    THEY    TEACH. 

General  Definitions  and  Divisions  of  the  Subject. 

S~^\  EOLOGY,    as   a  term,  is  derived  from   ^,   the  earth,  and 
VJT"  X6-(oq,  a  discourse. 

As  a  science,  it  treats  of  the  earth's  Constitution,  Condition, 
History,  and  Adaptations  to  human  wants. 

The  following  scheme  .shows  the  logical  subdivisions  of  the 
science: 

Constitution, 

Material  (I.  Lithological). 
Mechanical  (II.  Structural). 
Condition, 

Temperatures, 
Solidity  or  Fluidity, 
Rigidity. 

History,  and  its  Evidences, 
Grounds  of  Inference, 

Existing  Dynamic  Agencies, 
Records  of  Former  Actions, 
Thermal, 
Chemical, 
Mechanical, 
Organic. 

(IV.    Palaeontological). 
(V.    Formational). 

Succession  of  Events  (VI.   Historical). 
Adaptations  (VII.   Economical). 

245 


246  GEOLOGICAL   STUDIES. 

The  terms  above  appended  in  parentheses  are  the  general 
divisions  of  the  subject  which  will  be  employed  in  the  following 
synoptical  treatment.  They  may  be  defined  as  follows: 

I.  LITHOLOGICAL  GEOLOGY.     That  division  of  Geology  which 
treats  of  the  elementary  and  mineralogical  constitution  of   the 
Rocks,  and  their  mechanical  condition. 

II.  STRUCTURAL  GEOLOGY.     That  division  of  Geology  which 
treats  of    the  Superposition,    Succession,    Attitudes,   Accidents, 
and  Classification  of  Rocks,  both  Stratified  and  Unstratified. 

III.  DYNAMICAL  GEOLOGY.     That  division  of  Geology  which 
treats  of  the  Forces  and  Modes  of  Action  which  have  produced 
the  results  witnessed. 

IV.  PALAEONTOLOGY.     That  division  of  Geology  which  treats 
of    the  Organic  Beings,   vegetable   and   animal,   which  lived   in 
former  ages  of  the  world. 

V.  FORMATIONAL  GEOLOGY.     That  division  of  Geology  which 
treats  of  the  successive  systems  of  rocks  and  their  subdivisions, 
and  indicates  the  order  of  distribution  of  fossil  remains  through 
them.     (Divisions  IV  and  V  furnish  the  principal  data  of  Division 
VI.) 

VI.  HISTORICAL  GEOLOGY.     That  division  of  Geology  which 
narrates  the  succession  of  terrestrial  events,  as  induced  from  the 
data  supplied  by  the  preceding  divisions,  and  as  deduced  from 
the  recognized  principles  of  the  science. 

VII.  ECONOMIC  GEOLOGY.     That  division  of  Geology  which 
enumerates,  describes,  and  locates  the  various  mineral  substances 
possessing  utility  for  man,  and  explains  the  methods  of  extract- 
ing them  from  the  earth,  and  reducing  them  to  an  available  con- 
dition. 

In  the  following  sketch,  none  of  the  above  divisions  can  be 
carried  beyond  a  very  elementary  treatment,  and  two  of  them 
must  be  dismissed  with  references  to  Studies  in  Part  I. 

That  part  of  the  earth  which  is  accessible  to  our  investigations 
is  called  the  crust.  Nearly  the  whole  of  the  earth's  crust  is  in  a 


GENERAL   DEFINITIONS   AND   DIVISIONS.  247 

mineral  condition.  A  "mineral  is  a  definite  chemical  compound, 
not  depending  on  the  presence  of  life  for  its  maintenance.  A 
rock  is  any  mass  of  mineral  matter.  Most  of  the  matter  of  the 
rocks  has  been  arranged  through  the  action  of  inorganic  forces; 
but  some  portions  of  it  are  of  organic  origin  ;  though  nothing 
which  can  be  said  to  form  a  part  of  the  earth  is  properly  organic. 
A  rock  is  not  necessarily  solid. 


CHAPTER  I. 
LITHOLOGICAL  GEOLOGY  (PETROGRAPHY); 

OR,    WHAT    HAS    BEEN   LEARNED    ABOUT    THE    MATERIALS    OF    THE 

EARTH. 

[The  attention  already  paid  to  the  subject  in  Part  I  renders  it  unnecessary  to  intro- 
duce a  complete  summary  in  this  place,  the  more  so  since  summaries  and  tables  covering 
most  of  the  topics  may  there  be  found.] 

§  1.     Chemistry. 
Some  rudimentary  ideas  may  be  found  in  Study  IV. 

§  2.     Mineralogy. 

See  this  subject  explained  in  Studies  V,  VI.  See  the  Gen- 
eral Review,  the  Table  of  Composition  of  Minerals,  and  the 
Table  for  Determinations,  in  Study  VII. 

§3.     Kinds  of  Bocks. 

A  rock  is  a  mass  of  mineral  matter,  consisting  of  a  single  min- 
eral, or  an  aggregate  of  minerals.  Rocks  are  characterized  and 
distinguished  by  their  mineral  constitution,  their  physical  struc- 
ture, and  their  position  or  attitude  in  reference  to  other  rocks. 

1.   PHYSICAL  CONDITIONS  OF  ROCKS. 

(1)  Mineral  Constitution,  (a)  ESSENTIAL  CONSTITUENTS. 
Those  minerals  whose  presence  determines  the  specific  identity  of 
the  rock,  and  the  absence  of  one  of  which  would  make  it  some 
other  rock  species.  The  particular  specifications  belong  to  the 
definitions  of  the  rock-species  which  will  be  cited  beyond. 

(b)  ACCESSORY  CONSTITUENTS.  Those  minerals  which  are 
present  in  addition  to  the  essential  ones.  If  abundant  enough  to 
impart  any  conspicuous  or  otherwise  important  character,  they 
furnish  a  qualifying  term  for  the  name  of  the  rock,  as  shown 
below  : 


LITHOLOGICAL   GEOLOGY.  249 

Quartzose,  or  quartziferous,  containing  quartz.  The  qualify- 
ing constituent  may  be  of  such  variety  as  to  render  a  rock  ame- 
thystine, agatiferous,  chalcedonic,  flinty,  cherty,  or  jaspery. 
When  the  quartz  is  in  small  grains,  the  rock  is  arenaceous. 
When  it  is  intimately  disseminated,  or  combined,  the  rock  is 
silicious — a  term  often  used,  also,  as  equivalent  to  quartzose. 

Ferruginous,  when  stained  red  or  yellow  by  the  presence  of 
oxide  of  iron.  If  distinct  grains  of  haematite  or  limonite  are 
present,  the  rock  is  hcematitic,  or  limonitic. 

Pyritous,  or  Pyritiferous,  containing  pyrites. 

Saliferous,  containing  halite,  either  crystalline,  or  in  solution. 

Feldspathic,  or  Felsitic,  containing  feldspar;  but  the  latter 
term  may  be  restricted  to  the  presence  of  feldspar  in  the  state  of 
a  matrix,  or  ground  holding  other  minerals  imbedded  or  inti- 
mately mixed;  but  in  this  sense  felsitic  is  only  the  adjective  form 
of  felsite. 

JTaolinic,  containing  kaolin.  Micaceous,  having  disseminated 
scales  of  mica.  Hydromicaceous,  having  disseminated  hydro- 
mica.  Talcose,  or  Talcitic,  having  talc  in  scales  or  grains.  Ser- 
pentinous,  containing  serpentine.  C/iloritic,  containing  chlorite. 

Amphibolic,  containing  arnphibole.  Varieties  of  this  are 
hornblendic,  tremolitic,  and  actinolitic. 

Pyroxenic,  containing  pyroxene.  Varieties  are  augitic  and 
dialing  ic. 

Tourmalinic,  containing  tourmaline.  Fpidotic,  containing 
epidote.  Garnetiferous,  containing  garnets. 

Calcitic,  or  calciferous,  containing  calcite.  But  when  calcite 
is  present  in  an  impure  or  amorphous  condition,  the  rock  is  com- 
monly described  as  calcareous.  This  term  is  also  used  when 
calcite  is  the  essential  ingredient. 

Dolomitic,  containing  dolomite.  Sideritic,  containing  sider- 
ite. 

Argillaceous,  having  some  clayey  matter  disseminated.  But 
when  mingled  in  undiscernible  particles,  or  in  a  state  of  intimate 
union,  the  term  aluminous  is  preferable. 

Carbonaceous,  with  carbon  disseminated,  generally  imparting 


250  GEOLOGICAL   STUDIES. 

a  dark  or  black  color.  Bituminous,  containing1  bitumen.  Petro- 
liferous, containing  petroleum. 

Many  of  the  same  terms  are  employed  to  express  the  essential 
constituents  of  rocks.  Thus  a  micaceous  rock  is  one,  also,  which 
has  mica  for  an  essential  constituent.  A  talcose  schist  is  one 
characterized  by  talc.  Ordinarily,  where  practicable,  the  essen- 
tial constituent  is  indicated  by  retaining  the  substantive  form  in 
a  compound  word.  Thus  mica-schist,  hornblende-schist,  having 
mica  or  hornblende  as  essential  constituent;  while  micaceous 
sandstone,  micaceous  hornblende-schist,  hornblendic  mica-schist, 
and  hornblendic  gneiss,  indicate  mica  and  hornblende  as  mere 
accessories.  It  would,  perhaps,  be  a  convenience  if  the  termina- 
tion -ose  (osus,  abounding  in)  were  employed  to  denote  an  essen- 
tial constituent,  in  distinction  from  an  accessory  one.  We  should 
then  have  rocks  characterized  as  micose,  calcarose,  serpentinose, 
augitose,  carbonose,  etc.,  in  distinction  from  others  simply  mica- 
ceous, calcareous,  serpentinous,  augitic,  carbonaceous. 

(2)  Physical  Constitution,  (a)  FRAGMENTAL  ROCKS  are 
such  as  are  composed  of  fragments  of  other  rocks.  Of  these,  a 

Conglomerate  is  composed  of  coarse  rounded  fragments  and 
pebbles;  and  when  of  the  size  of  mustard  seed,  with  some  smaller, 
it  is  a  grit.  A  cemented  mass  of  angular  fragments  is  a  breccia. 

Sandstone,  composed  of  fine  rounded  grains  —  generally  grains 
of  quartz  —  more  or  less  firmly  cemented. 

Granular  signifies  composed  of  grains.  Granite  is  a  granu- 
lar rock;  but  most  granular  rocks  are  not  granite. 

Earthy,  lustreless,  of  indistinguishable  particles  and  not  hard- 
indurated. 

Sand.  Fine  grains  of  any  sort  of  mineral  or  rock,  most  fre- 
quently silicious.  When  of  volcanic  origin,  it  is  Volcanic  sand 
or  Peperino,  derived  from  the  "  cinders  "  or  "  ashes  "  (commi- 
nuted lava)  produced  during  an  eruption.  When  the  ashes 
become  consolidated  they  constitute  volcanic  tufa.  None  of  these 
substances  have  any  fixed  constitution. 

(b)  CRYSTALLINE  ROCKS.  Consisting  chiefly  of  distinct  crys- 
tals or  fragments  of  crystals.  Careful  observations  show  that 


LITHOLOGICAL   GEOLOGY.  251 

this  condition  sometimes  results  from  solution  in  icater,  as  in 
depositions  from  springs;  sometimes  from  solidifying  from  fusion, 
as  in  lavas  and  other  erupted  rocks;  and  sometimes  through 
metamorphism  of  deposits  originally  fragmental,  as  in  the  com- 
mon crystalline  rocks. 

Phanerocrystalline,  having  the  separate  crystal  fragments 
visible  to  the  naked  eye,  or  with  a  simple  lens. 

Microcrystalline,  exceedingly  fine-grained,  requiring  a  com- 
pound microscope  and  thin  slices  to  distinguish  the  constituents 
(Rosenbusch). 

Cryptocrystalline,  when  no  magnifying  power  employed  on 
thin  sections  discloses  the  constituent  minerals;  while  at  the 
same  time,  the  whole  mass,  being  composed  of  doubly  refracting 
particles,  has  evidently  a  crystalline  texture  (Rosenbusch). 

Microfelsitic,  partly  crystalline,  but  with  an  optically  iso- 
tropic  or  uncrystalline  base,  used  especially  for  felsites. 

Colloid  (like  glue),  glassy  and  homogeneous  under  high 
powers.  When  a  rock  of  colloid  texture  reveals  lines  suggesting 
a  flow  of  molten  matter,  these  are  styled  fluidal^  and  the  texture 


Porphyritic,  having  distinct  crystals  disseminated  through  a 
mass  of  some  other  kind,  either  phanerocrystalline  or  cryptocrys- 
talline.  If  the  disseminated  crystals  are  of  feldspar,  we  say  sim- 
ply, the  rock  is  porphyritic;  and  if  the  base  is  also  felsitic,  the 
rock  is  porphyry.  But  if  the  disseminated  crystals  are  pyroxene 
or  hornblende,  we  say  the  rock  is  porphyritic  with  pyroxene  or 
with  hornblende. 

(c)  RELATIONS  OF  ROCKS  TO  MECHANICAL  AND  CHEMICAL 
ACTIONS.  Hardness  depends  on  the  adhesion  of  the  particles 
under  pressure.  Quartz  is  hard,  but  gypsum  is  soft. 

JBrittleness  is  determined  by  the  readiness  of  the  particles  to 
separate  under  a  sudden  shock,  like  a  blow  with  a  hammer. 
Quartz  is  brittle  though  hard. 

Toughness  is  reluctance  of  particles  to  separate  under  a  sud- 
den shock  or  blow.  Hornblende,  pyroxene  and  serpentine  are 
tough,  though  more  or  less  soft. 


252 


GEOLOGICAL   STUDIES. 


Compactness  is  closeness  of  texture;  but  it  does  not  neces- 
sarily make  a  hard  or  tough  rock.  Serpentine  is  compact  though 
soft,  and  a  granular  quartzite  is  hard,  though  not  always  com- 
pact. Porosity  is  the  reverse  of  compactness. 

Friability  is  incoherence  of  parts.  The  parts,  however,  may 
possess  any  degree  of  hardness,  as  in  friable  sandstones. 

Durability  is  absence  of  disposition  to  change  under  the 
influences  exerted.  Against  durability  is  solubility  of  the  rock 
(like  limestone  or  gypsum),  or  of  the  cementing  material  of  its 
parts,  as  the  caloite  in  some  sandstones;  also  porousness,  which 
admits  water  to  augment  its  solvent  action,  and  permits,  also,  the 
entrance  of  frost  to  exert  its  mechanical  action. 

(3)  Stratified  and  Unstratified  States,  (a)  The  Strati- 
fied Condition.  The  materials  are  arranged  in  layers  or  beds 
called  strata.  These  may  exist  in  any  im- 
aginable attitude  or  condition.  Strata  are 
separated  by  narrow  openings.  These 
constitute  seams  when  filled  with  some 
special  sort  of  matter  (Fig.  193).  When, 
however,  a  very  thin  layer  between  two 
strata  is  a  result  of  sedimentation  it  is  a 
stratum  or  bed. 

Massive,  or  Thick-bedded,  indicates 
thick  or  heavy  strata.  The  term  has  no 
definite  limits,  but  we  may  say  the  strata 
are  a  foot  or  more  in  thickness. 

Thin-bedded  refers  to  thin  strata,  but 
has  no  precise  meaning.     We  may  say  the 
strata  are  four  inches  or  less  in  thickness. 

Shaly,  having  the  materials  deposited  in  very  thin  layers  or 
leaves  as  in  Fig.  194. 

Laminae  are  thin  subdivisions  of  strata.  The  layers  of  a 
shale  are  laminse. 

(b)  The  Unstratified  Condition.  This  exists  when  the  evi- 
dences of  stratification  are  wanting.  The  metamorphic  rocks, 
for  the  greater  part,  show  but  feeble  and  remote  signs  of  strati- 


FIG.  193.— SB  AMS  AND 
STRATA  —THICK-BEDDED 
AND  THIN-BEDDED,  WITH 

SEAMS   s,  s,  s,   between 
them. 


FIG.  194. —  LAMINATED 
STRATIFICATION  OB 
SHALT  STRUCTURE. 


LITHOLOGICAL   GEOLOGY.  253 

fication;  but  they  may  generally  be  discovered  in  (act)  the  seams 
which  intersect  the  rock-mass,  or  (bb),  lines  or  bands  in  the  dis- 
tribution of  the  mineral  constituents,  especially  mica,  hornblende 
and  pyroxene,  or  (cc)  in  some  other  inequality  in  the  distribution 
of  the  constituents  —  as  in  color  or  coarseness,  or  finally  (dd)  in 
the  fact  that  the  scales  and  lamellae  of  the  minerals  are  mostly 
disposed  in  one  direction.  (This  disposition  of  scales,  however, 
is  not  necessarily  the  result  of  sedimentation.) 

2.    METHODS  OF   STUDYING  ROCKS. 

(1)  Physical  Examinations.     Study  of  the  mineral  con- 
stituents through  their  physical  characters;  study  of  the  physical 
constitution  and  condition    of  the   rocks  ;  whether  stratified    or 
unstratified  (massive);  whether  crystalline,  uncrystalline,  colloid, 
or  porphyritic;  and  if  stratified,  whether  thick  or  thin  bedded. 
Here  are  embraced  also,  observations  of  color,  lustre  and  weight. 
This  is  the  method  most  available  for  the  elementary  student, 
and  hence,  the  one  here  employed. 

(2)  Microscopic   Examinations.     Thin,  transparent   or 
translucent  slices   of  rocks  prepared    as  indicated  on  page  205, 
and  examined  with  a  polariscope-microscope,  reveal,  by  the  optical 
and  minute    textural  characters  shown,   the  nature  of  the  con- 
stituent minerals.     This  is  accomplished  either  in  phanerocrystal- 
line  or  microcrystalline  rocks.     This  method  of  study,  introduced 
within  a  few  years,  is  constantly  growing  in  importance,  and  has 
become  indispensable   in   all   thorough  work.     But  we  must  be 
content  to  postpone  the  employment  of  it  to  an  advanced  course. 

(3)  Chemical  Examinations.     At  one  period  in  the  his- 
tory of  petrology  the  chemical  investigation  of  rocks  was  consid- 
ered, perhaps  justly,   as  the  most  exact  method  available;  and 
classifications  were  then  based  on  chemical  constitution.     Various 
expedients  for  arriving,  through  chemical  processes,  at  the  mine- 
ral ingredients  of  rocks,  have  been  proposed;  but  we  need  not 
explain  them  here.     Aggregate  or  average  chemical  characters 
are  still  employed,  as  in  the  terms  acidic  and   basic,  but  on  the 
whole,  chemical  methods  with  rocks    generally  have  fallen  into 


GEOLOGICAL   STUDIES. 

disuse.     It  may  be  necessary  to  add,  however,  that  in  the  study 
of  minerals,  chemistry  holds  the  first  place. 

(4)  Magnetic  Examinations.  These  have  some  repute 
in  the  study  of  certain  classes  of  rocks,  and  magnetic  indications 
are  probably  useful  in  explorations  for  beds  of  iron  ore  (see  T. 
B.  Brooks  in  Mich.  Geol.  Rep.,  1869-73,  Vol.  I,  Chap.  viii). 
But  it  is  not  appropriate  to  enter  upon,  the  subject  in  this  place. 

3.    MOST  IMPORTANT  SPECIES  OF  ROCKS. 

We  again  refer  the  reader  to  Part  I.  The  principal  species  and 
groups  of  rocks  are  treated  in  Studies  IX-XIII.  In  Study  XIV 
we  have  also  a  retrospect,  embracing  a  systematic  Table  of  Rock 
Structure,  a  Table  of  Rock  Compositions,  and  also  a  Table  for 
Rock  Determination.  The  latter  indicates  the  eleven  series  under 
which  the  rocks  may  be  classed. 


CHAPTER  II. 
STRUCTURAL  GEOLOGY  (GEOGNOSY)  ; 

OR,  WHAT  HAS  BEEN  LEARNED  ABOUT  FORMATIONS. 

§  1.     General  Definitions. 

FORMATION.  The  term  Formation  is  used  in  Geology,  as 
elsewhere,  to  express  the  abstract  conception  of  process  or  act 
of  forming.  It  is  also  used  in  a  concrete  and  specially  litholog- 
ical  sense  to  denote  that  which  has  been  formed.  It  is  the  litho- 
logical  result  of  an  action  or  concert  of  actions  producing  some- 
thing possessing  unity  and  completeness.  A  particular  "  forma- 
tion," though  it  may  be  a  constituent  of  something  which 
embraces  it,  has  limits  and  completeness  in  itself.  A  bed  of 
shale  is  a  formation,  and  so  is  a  bed  of  sandstone;  and  these  two 
may  be  so  affiliated  together,  and  so  differentiated  from  other 
beds  of  rocks,  as  to  constitute  a  formation.  A  doleritic  dike  is 
also  a  formation;  and  if  it  intersects  the  shale  and  sandstone,  the 
three  constitute  a  formation.  The  term  is  thus  general  or  com- 
mon, without  fixed  breadth  of  application.  The  term  terrane  is 
employed  in  a  sense  almost  identical. 

The  most  frequent  application  of  the  term  formation  is  to 
stratified  beds,  and  hence  ordinarily  it  refers  to  beds  belonging 
to  one  particular  interval  of  time,  as  the  "  Cretaceous  formation," 
the  "Potsdam  formation." 

Sedimentation.  The  deposition  of  rock  material  by  subsi- 
dence in  water. 

Stratification.  The  arrangement  of  rock  material  in  succes- 
sive layers.  This  generally  results  from  sedimentation. 

Layer.     A  single  sheet  of  sedimentary  material. 

Stratum.     A  series  of  layers  intimately  connected.     The  lay- 

255 


256 


GEOLOGICAL   STUDIES. 


ers  may  differ  in  color  or  fineness,  or,  within  small  limits,  in  ma- 
terial. The  term  bed  is  often  employed  in  the  same  sense.  A 
bedded  rock  is  a  stratified  rock. 

Seam.  The  parting 'plane  between  two  strata.  It  is  gener- 
ally in  the  nature  of  a  thin,  non-sedimentary  layer,  different  from 
the  contiguous  layers  above  and  below.  The  substance  of  seams 
is  often  clay,  less  or  more  bituminous,  or  even  pure  inspissated 
bitumen  or  coaly  matter. 

Fossil.  The  relic  or  trace  of  an  organic  being,  animal,  or 
plant,  embraced  in  the  substance  or  open  spaces  of  a  rock  or  a 
formation.  Rocks  containing  fossils  are  fossiliferous. 


§  2.     Accidents  of  Stratified  Bocks. 

1.  Accidents  of  Sedimentation.  The  terms  conglom- 
erate, arenaceous,  granular,  sandy,  shall/,  and  earthy  are  briefly 
defined  (p.  250)  in  explaining  terms  employed  in  rock  descrip- 
tions. It  is  only  nece-ssary  to  add  the  following  : 

Oblique  Lamination.  This  is  seen  when  the  lines  of  lami- 
nation are  inclined  to  the  plane  of  stratification.  The  same  in- 
clination of  the  laminae  may  persist  throughout  a  considerable 

extent  of  the  stra- 
tum (Fig.  195), 
or  may  change  at 
frequent  inter- 
vals. 

Ebb  and  Flow 
Structure.  Con- 
sisting of  layers 
of  various  kinds 

within  one  stratum,  some  being  irregu- 
lar, and  others  horizontally  or  obliquely 
laminated  (Fig.  196). 

Drift  Structures.  This  denotes  abrupt 
terminations  of  laminated  beds  and  ir- 
regular changes  in  inclination  of  laminae,  as  shown  in  Fig.  195. 


FIG.  195.— OBLIQUE  OB  CROSS 
LAMINATION  IN  POTSDAM 
SANDSTONE,  Wis.  (After 
Strong.)  The  horizontal 
strata  are  separated  by  the 
seams  s,  s,  s.  The  lamina- 
tion in  each  stratum  (except 
part  of  the  lower)  is  uncon- 
formable— oblique  and  irreg- 
ular. 


FIG.  196. —  EBB  AND  FLOW 
STRUCTURE.  (Foster  and 
Whitney.) 


STRUCTURAL    GEOLOGY. 


257 


Besides    its    occurrence   in   regularly  stratified   formations,   it   is 
everywhere  shown  in  the  "  Modified  Drift "  (see  Figs.  7,  8,  and  9). 

Ripple  Marks.  Ridges  like  miniature  waves  on  the  surface 
of  a  stratum.  They  are  often  seen  on  the  surface  of  sand  drifted 
by  the  wind. 

Rain  Prints.  Marks  of  rain  drops,  produced  when  the  stra- 
tum was  a  soft  beach  sediment. 

Mud  Flow.  Appearances  like  flowing  mud  on  the  surfaces 
of  strata.  (Compare  Fig.  199). 

2.  Accidents  of  Secondary  Origin.  Many  changes  have 
taken  place  in  the  structure  and  mechanical  condition  of  strata 
since  the  time  of  their  original  deposition. 

Mud  Cracks.  Irregularly  intersecting  fissures,  appearing  like 
cracks  produced  in  drying,  and  subsequently  filled  by  other  sedi- 
ments. The  filling  of  each  crack  shows  a  median  joint  or  fissure, 
as  if  the  deposit  had  flowed  down  each  of  the  opposing  walls, 
forming  layers  which  met  in  the  middle. 

Cone  in  Cone.  A  singular  and  unexplained  structure  seen 
in  some  argillaceous  strata,  having  lines  of  structure  arranged  in 
conical  or  trumpet- 
shaped  forms  in  sev- 
eral series,  which 
seem  to  be  associ- 
ated together  in 
nests. 

Lignilites,  Stylo- 

lites,   or  Toothed  Structure.     Partings  in  certain 
limestones  which  are  roughly  conformable  with  the          F       „ 
stratification,  but  have  their  surfaces  studded  with    TOOTHED  STRUC- 
tooth-like  projections,  which  interlock  from  oppo-       TUBE,  OFTEN 
site  sides,  and  appear  as  the  terminations  of  stri-      ^L* 
ated  or  furrowed  pegs  which  penetrate  the  rock 
vertically,  above  and  below,  and  at  a  distance  generally  less  than 
three  inches  become  confluent  with  it.     The  partings  and  the  peg- 
like  forms  are  generally  blackened  with  bituminous  matter. 


FIG.  197.— CONE  IN  CONE  STRUCTURE. 


258 


GEOLOGICAL   STUDIES. 


Concretionary  Structure.     This  consists  of  concentric  layers 
of  materials   around   some  centre,  at  which  may  be  found  fre- 


FIG.  199.  —  CALCAREOUS  CONCRETIONS. 
(From  the  Portage  Shales  of  northeastern  Ohio.) 

quently  a  crystal  or   some   organic  fragment.     Instead  of    con- 
centric layers,  the  structure  is  often  radiated.     Sometimes  these 

masses  show  shrink- 

a£e   cracks>   which 

-i  ,  , 

have  been  subse- 
quently filled,  and 
thus  form  what  are 
vulgarly  called  "tur- 
tle stones,"  and 
sometimes  "  septa- 
ria."  Kidney  iron 
stone  consists  of 
FIG.  200.—  JOINTED  STRUCTURE  SEEN  IN  ONONDAGA  LIME-  concretions  (see  p. 


STONE  AT 
uxem.) 


SPLIT  ROCK,"  NEAR  SYRACUSE,  N.Y.    (Van- 


^      Some  alumino- 
' 

calcareous  concre- 
tions assume  very  curious  forms,  four  of  which  are  shown  in  Fig. 
199.  Many  are  handsomely  spherical  or  spheroidal.  Others 
present  a  striking  resemblance  to  flowing  mud.  The  concre- 
tionary structure  can  often  be  traced  in  strata  where  no  sepa- 


STRUCTURAL   GEOLOGY. 


259 


rable  concretion  has  been  formed.  The  lines  pass  across  the 
bedding  planes  and  inclose  spaces  which  partake  of  the  general 
stratification,  thus  showing  that  the  structure  was  a  secondary 
result  (p.  48). 

Where  small  spherulitic  concretions  are  plentifully  dissemi- 
nated through  limestones,  the  latter  become  pisolitic  (pisum,  a 
pea),  or  oolitic  (aiov,  an  egg). 

Jointed  Structure.  The  presence  of  one  or  more  sets  of 
divisional  planes  or  cracks  which  pass  across  the  stratification, 
extending  to  great  depths,  and  divide  the  rock  mass  into  cuboidal 
segments.  These  planes  sometimes  extend  in  rigidly  fixed  direc- 
tions for  many  miles,  and  those  in  each  set  are  strictly  parallel. 

Slaty  Structure,  or  Slaty  Cleavage,  consists  in  a  system  of 
closely  crowded  joints  which  create 
a  tendency  in  the  rock  to  split  in 
thin  sheets,  as  in  roofing  slate.  This 
cleavage  generally  crosses  the  planes 
of  bedding,  but  sometimes  corre- 
sponds with  them. 

Polished  Faces,  "  Slickensides." 
Polished  surfaces  along  the  faces  of 
a  fissure  intersecting  the  stratifica- 
tion, caused  apparently  by  friction 
of  opposed  surfaces  resulting  from 
slight  movements  in  the  earth's 
crust. 

Sand  Blast  Action.  The  polishing  of  rock  surfaces,  especially 
of  pebbles  and  bowlders,  by  the  friction  of  dry  sand  driven  by 
the  wind. 

Metamorphism.  A  change  in  the  condition  of  a  sedimentary 
rock  by  which  the  lines  of  sedimentation  are  obscured  or  obliter- 
ated, the  fossils  destroyed,  and  a  crystalline  condition  superin- 
duced. The  work  of  metamorphism  has  been  accompanied  by  a 
softening  or  aqueous  semi-fusion  of  the  materials,  the  formation 
of  new  crystalline  combinations,  the  moulding  of  certain  crys- 
tals around  others  (as  quartz  around  feldspar),  and  sometimes  the 


FIG.  201. — SLATY  STRUCTURE,  AS 
SEEN  IN  SLATES  IN  COLUMBIA 
Co..  N.  Y.    (Mather.) 
The  strata  a,  6,  c,  d,  etc.,  are 
crossed     by     crowded     cleavage 
planes  parallel  with  each  other, 
but  wholly    independent    of   the 
stratification. 


260  GEOLOGICAL   STUDIES. 

squeezing  of  the  softened  rock  into  fissures,  imparting  to  it  the 
vein-like  condition  of  a  true  erupted  formation.  (See  further 
particulars  in  Chapter  III,  §  3,  (4).) 

3.  Attitudes. Of  Strata.  It  is  probable  that  most  strata 
were  originally  horizontal,  or  nearly  so.  Observations  upon 
modern  sedimentation  show  that  sediments  falling  upon  an  un- 
even bottom  tend  to  the  lower  levels  until  the  inequalities  dis- 
appear. After  that,  the  successive  sedimentary  sheets  are  parallel 
and  practically  horizontal. 

The  actual  attitudes  of  rocky  strata,  however,  are  generally 
at  a  wide  divergence  from  undisturbed  horizontality.  In  many 
instances  a  whole  formation,  over  hundreds  of  square  miles,  pre- 
sents a  regular  or  gently  undulating  inclination.  In  other  cases, 
in  addition  to  the  general  inclination,  the  subordinate  beds  and 
layers  have  undergone  a  complicated  disturbance. 

Outcrop  is  the  appearance  of  a  stratum  or  formation  at  the 
surface.  Generally  the  outcrop  is  the  weathered  termination  or 
edge  presentation  of  strata  which  from  that  point  disappear 
beneath  other  formations. 

Dip  is  the  direction  in  which  a  stratum  descends  below  the 
horizontal  plane.  The  amount  of  the  dip  is  the  angle  made  with 
the  horizon. 

Strike,  Trend,  or  Axis  is  the  direction  in  which  the  outcrop 
continues  along  the  surface.  If  the  surface  were  level,  the  strike 
would  always  be  at  right  angles  with  the  direction  of  the  dip. 
So,  also,  if  the  slope  of  the  surface  were  in  the  direction  of  the 
dip  or  the  opposite  direction. 

Breadth  of  Outcrop.  This  is  the  distance,  measured  along 
the  surface  of  the  earth,  between  the  upper  and  under  sides  of 
the  formation.  Its  amount  depends,  in  a  level  region,  on  the 
thickness  of  the  formation  and  the  steepness  of  the  dip.  More 
generally  it  depends  on  the  thickness  of  the  formation  and  the 
angle  of  plunge  beneath  the  surface.  This  is  equal  to  dip  plus  the 
angle  of  inclination  of  the  surface  if  it  rises  in  the  direction  of 
the  dip,  and  minus  this  angle  if  the  surface  descends  in  the 
direction  of  the  dip.  The  relation  is  such  that 


STRUCTURAL    GEOLOGY. 


261 


Breadth  of  Outcrop  = 


Thickness  of  Formation 


Sine  of  Plunge. 
Hence,  when  the  plunge  is  90°, 

Breadth  of  Outcrop  =  Thickness  of  Formation. 
Hence,  also, 

Thickness  of  Formation  =  Breadth  of  Outcrop  X  Sine  of 
Plunge. 

Synclinal  Axis.  This  is  a  line  toward  which  the  strata  dip 
from  opposite  sides.  (See  Fig.  50.)  A  general  descent  of  the 
strata  from  opposite  sides,  across  a  broad  region,  regardless  of 
subordinate  flexures,  is  a  Geosynclinal  arrangement. 

Anticlinal  Axis.  The  line  from  which  the  strata  dip  in 
opposite  directions  (Fig.  45).  A  G-eanticlinal  expresses  a  gen- 
eral anticlinal  tendency  of  strata  over  a  wide  extent,  independ- 
ently of  subordinate  undulations  of  the  surface. 

Quaquaversal  Dip.  A  dip  in  all  directions  from  a  common 
point. 


FIG.  202.— A  FLEXURE  BECOMING  A  FAULT.    (Powell.) 

The  disturbances  to  which  the  earth's  crust  has  been  subjected 
have  not  only  tilted  the  strata,  but  subjected  them  to  extensive 
fracture.  A  line  of  fracture  generally  pursues  a  direct  course 
for  several  miles  —  sometimes  even  a  hundred  miles  or  more. 

A  Fault  or  Dislocation  is  a  displacement  of  strata  along  a 
fracture,  which  destroys  the  correspondence  of  the  strata  on 


262 


GEOLOGICAL   STUDIES. 


opposite  sides.  They  are  common  in  mountainous  regions. 
Faults  may  attain  to  displacements  of  many  thousand  feet.  A 
fault  results  from  an  upthrow  on  one  side  or  a  downthrow  on  the 
other.  Faults  are  illustrated  in  Figs.  86,  34. 


FIG.  203.— INVERTED  SUPERPOSITION. 

A  Flexure  is  a  bending  of  the  strata.  When  the  flexure  is 
abrupt,  or  considerable  in  vertical  extent,  it  often  results  in  frac- 
ture and  faulting.  In  many  instances  a  fault  may  be  traced  into 
a  shattered  flexure,  and  thence  to  an  unbroken  flexure,  which  sttll 
beyond  dies  out. 

A  Fold  is  a  series  of  strata  uplifted  to  a  more  or  less 
elevated  anticlinal  axis.  Generally,  the  steepness  of  the  dip  is 
greater  on  one  side  of  the  fold  than  on  the  other.  In  other 

words,  the  fold 
is  pushed  over. 
Sometimes  the 
inclination  be- 
comes such  as  to 
give  the  strata 
on  one  side  a  ver- 
tical position 
(Figs.  294,  293), 
or  even  an  in- 
verted dip  (Fig. 
203).  The  fold  is 
FIG.  204. — CONTORTED  STRATIFICATION  OF  SCHISTS  IN  WEST-  then  said  to  be 

CHESTER  Co.,  N.  Y.   (Dana.)  overturned.    The 

strata  6,  5,  4,  3,  2,  1  on  the  left  of  the  figure  follow  each  other 
in  an  inverted  order,  1,  2,  3,  4,  5,  6,  on  the  right  of  the  axis  of 
the  fold  ;  and  the  strata  in  the  latter  series  are  bottom  side  up. 


STRUCTURAL   GEOLOGY.  263 

Plication,  Crumpling,  Contortion.  In  many  regions  strata  are 
not  only  tilted  and  folded,  but  wrinkled  or  plicated  in  an  irregu- 
lar and  remarkable  manner,  as  illustrated  in  Figs.  £04  and  205. 
Such  crumplings  naturally  suggest  the  exertion  of  enormous 
lateral  pressure  upon  softened  strata. 

Conf or  inability  is  parallelism  of  the  sedimentary  planes  of 
strata.  When  the  dip  of  a  formation  is  different  from  that  of  a 
formation  on  which  it  is  superimposed,  the  two  are  unconform- 
able.  Generally  the  lower  formation  has  the  greatest  dip;  and 
this  demonstrates  that  it  has  experienced  at  least  one  more 
upthrow  than  the  overlying  formation  (Figs.  293,  107,  298). 
Sedimentation  over  a  surface  rendered  irregular  by  previous 


FIG.  205.— CONTORTED  STRATA  OP  POTSDAM  SANDSTONE  IN  ST.  LAWRENCE  COUNTY, 
K.  Y.    (Emmons.) 

wearing  results  also  in  a  species  of  unconformability  known 
as  a  break,  or  a  breach  of  stratigraphical  continuity.  (Figs. 
302,  298.) 

4.  Erosion  of  Strata.  All  rocks  exposed  to  the  action  of 
the  elements  undergo  continued  wastage.  Their  exposed  sur- 
faces disappear  through  solution  or  disintegration.  The  rate  of 
disappearance  depends  on  the  intensity  of  the  action  and  the 
power  of  the  rock  to  resist  it.  Hence  the  wear  is  irregular,  and 
in  the  course  of  geologic  cycles  very  striking  results  have  been 
produced.  Some  of  these  are  illustrated  in  Figs.  75,  83,  32,  35. 

Denudation  is  the  wasting  away  of  the  rocks  through  the 
action  of  the  elements,  aided  sometimes  by  extraordinary  geo- 
logical action,  like  earthquakes,  floods,  and  lava  torrents. 

Cir cum  denudation  is  a  wasting  on  all  sides  of  a  mass  of 
rocks,  leaving  it  to  stand  at  or  near  its  original  altitude,  while 
the  surrounding  rock  masses  have  been  removed. 


264  GEOLOGICAL   STUDIES. 

An  Outlier  is  an  outstanding  mass  of  rocks  resulting  from 
circumdenudation.  Figs.  35,  355,  301. 

"    Erosion,  in  the  more  special  sense,  refers  to  mechanical  action 
localized  along  a  river  valley  or  sea  or  lake  coast. 

Corrasion  is  that  part  of  erosion  which  results  from  the 
impact  of  transported  materials  against  the  surfaces  undergoing 
erosion. 

§  3.     Conditions  of  Unstratified  Rocks. 

1.  The  Erupted  Condition.  The  state  of  rock  material 
which  has  issued  in  a  molten  condition  through  rents  in  the 
earth's  crust,  like  lavas  from  modern  or  ancient  volcanoes,  or 
lava-like  materials  from  ancient  fissures  and  rents.  Descriptions 
have  been  given  in  Study  XXIII  of  several  important  examples. 
The  basaltic  structure  belongs  to  erupted  rocks.  It  consists' in 
closely  fitting  polygonal  prisms  of  basalt,  of  which  some  notable 
examples  exist  in  the  "  Giant's  Causeway"  and  "  Fingal's  Cave"; 
also  on  the  banks  of  the  Hudson  and  Columbia  rivers. 

Erupted  beds  are  often  overlaid  by  other  erupted  beds  of 
later  origin,  giving  a  truly  bedded  structure,  which  must  not  be 
confounded  with  sedimentary  bedding.  Volcanic  bedding  occurs 
especially  on  the  slopes  of  volcanoes.  The  bedded  structure  is 
also  common  among  the  ashes  and  cinders  ejected  from  volcanic 
openings,  as  in  California  and  Washington.  Some  of  the  con- 
glomerate beds  of  Keweenaw  Point,  Lake  Superior,  are  thought 
by  some,  but  not  by  the  latest  writers,  to  be  ancient  volcanic 
ejections,  though  interbedded  with  strata  of  undoubted  aqueous 
origin. 

Amygdules.  Small  almond-shaped  or  spheroidal  cavities 
filled  with  infiltrated  mineral  matter  of  various  kinds.  Sometimes 
one  sort  fills  the  cavity,  and  sometimes  various  sorts  have  been 
introduced  in  successive  concentric  layers.  Rocks  thus  formed 
are  amygdaloids.  (Fig.  80.)  They  occur  in  the  more  super- 
ficial parts  of  anciently  igneous  formations.  The  cavities  are 
supposed  to  have  been  originally  filled  with  steam. 

Pseud- Amygdules.     The  mineral  filling  of  rock  cavities  which 


STRUCTURAL   GEOLOGY.  265 

by  some  means  were  enlarged  beyond  the  dimensions  of  an  origi- 
nal vapor  vesicle;  or  even  of  cavities  formed  where  no  vapor  vesi- 
cle existed.  Sometimes  these  cavities  run  together. 

Metasomatic  Change.  The  displacement  on  a  large  scale  of 
the  chemical  substances  of  the  minerals  constituting  a  rock,  and 
the  substitution  of  other  chemical  substances.  The  transforma- 
tion of  augite  into  uralitic  hornblende  (having  the  form  of  augite 
and  cleavage  of  hornblende),  so  commonly  observed  in  the  North- 
west, is  part  of  such  a  process.  Similarly  we  find  chlorite,  viri- 
dite,  and  other  substances  appearing  as  secondary  products.  By 
such  and  analogous  changes  the  whole  body  of  a  formation  may 
become  changed.  All  regional  metamorphism  of  stratified  rocks 
is  essentially  of  this  character. 

2.  The  Intrusive  Condition.     This  term  is   commonly 
applied  to  the  condition  of  rock  material  intruded  in  a  molten 
state,  between  strata.     This  is  illustrated  in  Fig.  46.     The  tra- 
chytic  intrusions  of  the  Henry  Mountains  are  illustrations  on  a 
large  scale.     See  Study  XXIV,  page  150. 

3.  The  Vein  Condition.     A  Vein,  in  the  general  sense, 
is  a  fissure  in  the  earth's  crust  filled  with  mineral  matter  different 
from  that  of  the  fissured  rock  (Figs.  96,  97,  98).    When  the  fissure 
is  straight  and  filled  with  matter  injected  in  a  molten  state,  it 
forms   a   dike    (Figs.   77,   79,   83).      When   the   filled  fissure    is 
more  or  less  sinuous  and  irregular,  it  forms  a  vein  in  the  more 
restricted   sense.     Such   veins  may  be  filled   with   granite,  por- 
phyry, or  other  rocks  commonly  reputed  of  the  igneous   class. 
(Fig.  46.)     Most  commonly,  however,  the  filling  of  a  true  vein 
consists   of  layers   of  various  mineral   matters  on   the  opposite 
walls,  in  corresponding  succession  (Figs.  99,  100).     This  subject 
is  further  elucidated  in  Study  XXVII. 

§  5.     Classification  of  Formations. 

1.  Evidences  of  Relative  Age.  (1)  From  Superpo- 
sition. Evidently  the  sediments  were  originally  laid  down  in  the 
order  of  age.  Unless  subsequently  overturned,  the  relative  ages 
of  the  strata  would  be  indicated  by  their  order  of  superposition. 


266 


GEOLOGICAL   STUDIES. 


Cases  exist,  however,  in  which  an  upraised  fold  has  been  over- 
turned on  a  vast  scale.  Here  the  ages  of  the  strata  on  the  under 
side  of  the  fold  must  be  the  reverse  of  their  order  of  superposi- 
tion (Fig.  203).  These  circumstances  create  great  difficulties  for 
the  practical  geologist. 

The  faulting  of  strata,  in  some  cases  where  the  accident  is 
concealed,  gives  rise  to  embarrassments  in  determining  the  true 
order  of  superposition.  Here,  in  Fig.  206,  the  strata  are  faulted 


'^J^ff 


"     206  F  d       208 

FIG.  206— REPETITION  OP  STRATA  BY  FAULTING.  Faulted  limestone  at  Barnegat, 
Dutchess  Co.,  N.  Y.  (Mather.) 

FIG.  207 — DEPOSITION  SUBSEQUENT  TO  FORMATION  or  DIKE  OR  FAULT.  Section  in 
Calabria.  (Cortese.)  Fi,  Filadelfia.  g,  Granitic  rocks,  d,  Dioritic  rocks,  pi,  Plio- 
cene strata.  F,  Fault  intersecting  the  Apennines,  older  than  the  Pliocene  epoch. 

FIG.  208.  DIKE  AND  OVERFLOW  WITH  SUBSEQUENT  SEDIMENTATION,  d,  Dike.  «,  Over- 
flow, a,  6,  Later  sediments. 

at  b  m,  c  m,  d  m,  etc.,  so  that  the  stratum,  a,  after  dipping 
beneath  the  surface,  is  brought  to  the  surface  again  at  b,  c,  d, 
etc.,  and  thus  appears  to  be  four  or  more  different  strata  of  the 
same  kind. 

(2)  Evidence  from  Fossils.  Geological  investigation  has 
shown  that  the  stratified  formation  of  each  successive  period 
is  characterized  by  particular  fossil  remains.  Having  learned  by 
extensive  observation  what  are  the  characteristic  fossils  of  each 
formation,  the  discovery  of  any  of  these  fossils  may  be  taken  as 
evidence  of  the  age  and  position  of  the  formation  in  which  they 
occur.  In  general,  the  evidence  of  age  when  skilfully  deduced 
from  fossils,  is  considered  next  in  value  to  that  derived  from 
observed  superposition.  But  the  value  of  palaeontological  evi- 
dence diminishes  with  the  increase  of  distance  between  the  local- 
ities compared,  and  with  the  divergence  of  the  physical  condi- 
tions under  which  the  two  faunas  existed  while  living.  The 


STRUCTURAL   GEOLOGY. 


267 


nature  of  those  conditions  is  indicated  in  part  by  the  kind  of 
rock  holding  the  fossils. 

(3)  Evidence  from   Intersections   of  Vein   Matter.     It  is 
at   once   intelligible   that   a  vein  or  dike  interrupted  or  cut   off 
by  another  vein  or  dike  existed  before  the  one  which  cuts  it  off. 
On  this  principle,  the  chronological  succession  of  a  considerable 
number  of  dikes  may  sometimes  be  determined.     A  remarkable 
case  is  illustrated  in  Study  XXVII,  Fig.  98.     In  some  cases  a 
dike  or  fault  may  be  seen  intersecting  the  lower  strata,  but  ter- 
minating before  reaching  the  surface.     In  the  case  shown  in  Fig. 
207,  the  evidence  is  that  the  dike  or  fault,  F,  is  older  than  the 
formations  pl^  and  g  and  d  below  pi.     The  proof  of  anteriority 
of  a   dike   is  clearer  when  there  remains  a  mass  of  overflowed 
matter,   e,   Fig.    208,   resting    on   the    ancient   surface   and   now 
included  between  the  older  strata  and  the  later  a,  deposited  upon 
it.      In    some    cases,   however,   the    molten    matter   e   has   been 
intruded  between  the  strata  after  the  deposition  of  the  overlying 
strata,  as  in  laccolitic  mountains,  Figs.  82,  83.     Compare  also  the 
porphyry  intrusions,  Fig.  46. 

(4)  Method  of  Combining  the  Observations.     Suppose  careful 
determinations  of  strata  have  been  made  in  many  places.     Sup- 
pose the  various  formations  have 

been  so  studied  and  identified  that, 
separately,  each  may  be  charac- 
terized and  named.  Suppose  that 
in  one  region  (1),  as  indicated  in 
the  annexed  scheme,  the  forma- 
tions studied  may  be  designated 
E,  F,  G,  H;  in  another  (2),  B,  C, 
E,  F,  G;  in  another  (3),  A,  L,  M, 
N,  O;  in  another  (4),  H,  I,  J,  N; 
in  another  (5),  B,  D,  K,  M,  and  so 
Then,  correlating  these  sev- 


(1) 

(•2) 

(3) 

(4) 

(5) 

VI 

A 

A 

B 

B 

B 

C 

C 

D 

D 

E 

E 

E 

F 

F 

F 

G 

G 

G 

H 

II 

H 

I 

I 

J 

J 

K 

K 

L 

L 

M 

M 

M 

N 

N 

N 

0 

0 

on. 


eral  series  of  strata,  we  should  have  them  stand  as  shown  in  the 
columns  headed  (1),  (2),  (3),  (4),  (5).  Obviously,  then,  the  com- 
plete succession  deducible  from  these  collated  series  is  that  shown 


268 


GEOLOGICAL   STUDIES. 


in  the  column  headed  (VI).  Now,  wherever  any  formation,  as  F, 
is  recognized  by  its  fossils,  or  otherwise,  we  know  its  position  in 
the  complete  series;  and  we  know  what  should  follow  next  above, 
and  what  next  below.  And  whenever  the  succession  is  incom- 
plete as  in  (1),  we  know  the  four  newer  formations  are  wanting; 
when  it  is  like  (2),  we  know  the  newest,  and  also  formation  D, 
are  wanting;  when  like  (3),  we  note  a  wide  gap  between  A  and 
L,  and  so  on. 

2.  The  Cycle  of  Sedimentation.    The  phenomena  thus 
designated  are  also  connected  with  the  relative  ages  of  strata. 

CYCLES  OF  SEDIMENTATION. 


Palaeo- 
zoic 

Systems. 

Coarse  Frag-- 
mental. 

Fine  Fragrxnen- 
tal. 

Calcareous. 

Calcareo-Frag-- 
mental. 

f| 

£o 

Parma  Conglomer- 
ate. 

Coal  Measures. 
(Broken  into  many 
short  epochs.) 

Laramie 
Limestone. 

Permian  Group. 

«    • 
-  - 

fi 

Waverly  Sandstone. 
(Marshall  Phase.) 

Waverly    Group. 
(Chouteau  Phase.) 

Mountain 
Limestone. 

False  Coal  Meas- 
ures. 

M 
Ss 

Oriskany    Sand- 
stone. 

Schoharie  Grit. 

Corniferons 
Limestone. 

Hamilton  Gron  p, 
followed  by  Che- 
mung. 

15 

S3   « 

Medina  Sandstone. 
Oneida  Conglomer- 
ate. 

Niagara  Shale. 
Clinton  Group. 

Niagara 
Limestone. 

Salina  Group. 

*i 

Sg 

Potsdam  Sandstone. 

Calcif  erous  and 
Chazy. 

Trenton  Group. 

Cincinnati  Group. 

It  expresses  the  general  fact  that  the  series  of  strata  is  made  up 
of  repetitions  of  a  smaller  series;  and  the  smaller  series  has  below, 
a  coarse  fragmental  member,  followed  by  a  fine  fragmental  mem- 
ber, and  so  on  in  fixed  order,  and  terminating  with  a  calcareous 
or  calcareo-fragmental  member.  This  order  of  succession  is  con- 
nected, as  we  shall  hereafter  see,  with  the  periodical  occurrence 
of  greater  and  less  energy  in  the  processes  of  sedimentation. 
This  order  is  not  to  be  conceived  as  always  sharply  defined;  but 


STRUCTURAL   GEOLOGY.  269 

the  general  expression  of  it  in  the  entire  series  of  strata  is  suf- 
ficiently striking  to  be  noted  as  a  fact  of  geological  significance. 
Anticipating  the  explanations  of  the  names  of  formations,  we 
here  subjoin  (page  268)  a  tabular  exhibit  of  the  large  cycles  real- 
ized in  the  succession  of  geological  groups. 

The  oldest  formation  here,  the  Potsdam  Sandstone,  is  placed, 
as  usual,  at  the  bottom.  This  is  "coarse  fragmental."  At  the 
right  is  placed  the  next  following  formation,  the  Calciferous  and 
Chazy,  and  these  together  represent  the  "  fine  fragmental " 
member  of  the  Cambrian  Cycle.  Next  to  the  right  stands  the 
Trenton  Group  (proper),  and  this  is  the  great  "calcareous" 
member  of  this  cycle.  Finally,  still  further  to  the  right,  is  the 
Cincinnati  Group,  which,  as  we  shall  see,  is  mixed  calcareous  and 
argillaceous,  and  thus  stands  for  the  last  member  of  the  cycle. 
The  next  formation  in  ascending  order  is  the  Oneida  Conglom- 
erate and  Medina  Sandstone.  This  is  coarse  fragmental  again; 
and  thus  commences  a  new  cycle.  On  its  completion,  a  third 
cycle  begins  with  the  Oriskany  Sandstone.  Thus  the  whole  Pal- 
aeozoic series  is  composed  of  five  Sedimentary  Cycles.  The  expla- 
nation of  the  Cycle  belongs  to  Dynamical  Geology. 

3.  General  Terms  Employed  in  Classification.  (1) 
Categories  of  Time  and  Strata.  On  such  grounds  as  have  been 
explained,  the  whole  series  of  strata  forming  the  stratified  crust 
of  the  earth  may  be  divided  into  general  and  subordinate  assem- 
blages. The  object  of  the  classification  is  to  give  expression  to 
the  history  of  events  in  the  life  of  the  earth.  These  events  have 
been  both  inorganic  and  organic.  There  has  been  a  series  of 
transformations  of  the  earth's  physical  aspect,  and  a  correspond- 
ing series  of  transformations  of  the  organic  populations  which 
have  inhabited  the  surface.  The  only  records  of  these  great 
events  are  preserved  in  the  rocks.  They  are  a  part  of  the  rocks. 
The  epochs  of  more  energetic  action  in  the  transforming  agencies 
have  been  marked  by  coarse  fragmental  deposits;  the  long  peri- 
ods of  repose  and  luxuriance  of  organic  production  are  symbol- 
ized by  the  great  accumulations  of  limestone.  The  same  events 
which  changed  the  aspect  of  the  physical  world  had  some  connec- 


270  GEOLOGICAL   STUDIES. 

tion,  at  least,  with  changes  in  the  aspect  of  the  organic  world. 
Thus  a  classification  of  the  rocks  is  a  marking  off,  also,  of  the 
stages  in  the  history  of  life. 

At  certain  epochs  the  lithological  and  palaeontological  breaks 
are  found  exceedingly  profound.  These  divide  the  history  of  the 
world  since  sedimentation  began,  into  a  succession  of  grand  Eras 
or  ^Eons.  Correspondingly,  they  give  us  the  greater  divisions 
in  the  succession  of  events.  There  are  two  conceptions  in  geo- 
logical classification,  time  and  events,  and  the  events  must  corre- 
spond to  the  time.  The  rocks  are  the  records  of  the  events.  So  a 
grand  division  of  time  gives  us  a  grand  division  of  the  rocks  and 
a  grand  division  in  organic  life.  The  general  designations  of 
these  grand  divisions  are  JEon  (sometimes  Era}  in  reference  to 
time,  and  Great  System  in  reference  to  strata.  The  type  of 
organization  corresponding  has  received  no  general  designation. 
The  divisions  of  an  ^Eon  are  designated  Ayes,  and  the  divisions  of 
a  Great  System  are  generally  known  as  Systems.  So  Ages  are 
further  divided  into  Periods,  and  Systems  are  divided  into  Groups. 
When  we  carry  the  division  farther,  Periods  are  divided  into 
Epochs,  and  Groups  into  Stages.  This,  at  least,  is  the  general 
system  of  nomenclature  employed  in  this  work,  and  conforms  very 
closely  with  general  usage  in  America.  Attempts  have  been 
made  by  an  International  Geological  Commission  to  unify  the 
usage  of  different  nations,  but  the  recommendation  of  the  Com- 
mission is  unfortunately  one  not  likely  to  command  the  accept- 
ance of  American  geologists  in  consequence,  partly,  of  its  wholly 
needless  changes  in  the  use  of  terms. 

We  now  arrange  these  general  terms  in  their  proper  order  of 
subordination  for  convenience  of  the  student,  repeating,  for  con- 
venience of  reference,  the  table  on  page  108. 

Time  Divisions.  Sock  Divisions.  Examples. 

GREAT  SYSTEM.  PALAEOZOIC,  C^ENOZOIC. 

AGE.  SYSTEM.  CAMBRIAN,   TRIASSIC. 

Period.  Group.  Niagara,  Eocene. 

Epoch.  Stage.  Calciferous,  Champlain. 

Each  of  the  different  time  divisions  has  its  special  designation 


STRUCTURAL   GEOLOGY.  271 

as  Eozoic,  Palaeozoic.  The  same  special  names  apply  to  the  cor- 
responding rock  divisions.  So  we  may  say  "  Cambrian  Age  "  or 
"Cambrian  System";  "Niagara  Period  "  or  "  Niagara  Group." 
But  each  special  name  can  only  be  used  for  a  certain  category — 
an  ^Eon  or  a  Great  System;  an  Age  or  a  System,  and  so  on.  We 
should  not  say  the  "Cambrian  Period"  or  "Cambrian  Epoch"; 
the  "Palaeozoic  Age"  or  "Palagozoic  Period."  This  would  be 
like  giving  the  name  of  a  class  to  an  order  or  family.  But  this 
solecism  is  too  frequently  perpetrated  even  by  our  reputable 
writers.  We  shall  even  observe  grosser  negligence  in  employing 
time  designations  where  rock  designations  are  meant,  as  "  The 
Trenton  Period  is  composed  of  calcareous  rocks,"  instead  of 
"Trenton  Group." 

(2)  Stratigraphical  Gaps.     It   has  already  been  abundantly 
shown,  in  Study  XIX,  that  the  complete   series  of  formations 
underlies  the  earth's  surface  only  in  limited  regions.     In  other 
regions,  rocks  belonging  low  in  the  series  occupy  the  surface;  or 
at  least  rocks  formed  long  before  the  conclusion  of  the  work  of 
rock  making.     It  often  appears,  also,  that  the  series  of  forma- 
tions under  a  particular  region  is  deficient  in  more  than  the  upper 
portion  of  the  standard  series.     Some  of  the  lower  ones  are  found 
omitted,  as  illustrated  in  the  columns  (2),  (3),  (4),  and  (5)  in  the 
scheme  on  page  267-     This  forms  a  Stratigraphical  Gap. 

(3)  Geological    Horizon.     We    may,  however,   make   out  a 
statement  of  the  complete  series  of  formations.     Then  each  form- 
ation stands  in  a  particular  place.     That  is  its  horizon.     Wher- 
ever we  recognize  it,  the  same  formations,  save  the  occurrence  of 
gaps,  are  always  found  above,  and  the  same  below. 

(4)  Geological  Equivalents.     Whenever   we   find   the   same 
geological  horizon  in  two  localities,  however  separated,  the  form- 
ations in  the  two  regions  are  equivalent.     Very  likely  the  char- 
acters of  the  strata  will  be  different.     They  may  be  even  as  dif- 
ferent   as    sandstone    and   shale;     but    chronologically   they    are 
equivalent,  and  lie  in  the  same  geological  horizon.     Owing  to  the 
difference  in  the  nature  of  the  sediments,  the  species  of  molluscs 
included  may  be  partially  or  even  wholly  different,  and  thus  the 


272  GEOLOGICAL   STUDIES. 

palasontological  identification  be  defeated.  Many  such  cases  are 
known.  We  may  then  determine  equivalency  of  horizons  by  a 
wide-extended  study  of  orders  of  superposition,  as  illustrated  in 
the  scheme,  page  267;  or  we  may  identify  one  or  more  conspicu- 
ous fossil  types  not  observed  in  either  locality  to  range  above  or 
below  a  particular  stratum  or  formation;  or  finally,  the  experi- 
enced palaeontologist  may  detect  a  particular  expression  in  some 
of  the  fossils  or  in  the  collocation  of  the  fossils  in  the  two  places, 
which  will  serve  as  an  indication  that  the  strata  in  those  places 
belong  in  the  same  geological  horizon. 

(5)  Geological  Synonyms.     The   geology  of  the   earth   has 
been  studied  independently  in  different  regions.     Each  investi- 
gator has  determined  the  succession  in  his  region;  and  unless  he 
could  certainly  determine  the  equivalences  between  his  formations 
and  those  of  some  earlier-studied  region,  has,  according  to  cus- 
tom, bestowed  his  own  names  upon  them.     These  are  ordinarily 
geographical  designations.     The  name  points  to  some  locality 
where  the  formation   can   be  advantageously  studied.     Now,  in 
the  course  of  time,  it  becomes  certain  that  a  formation  named  in 
one  region  is  the   equivalent  of  a  certain   formation  differently 
named  in  another  region.     The  two  names  are  now  synonyms. 
Thus,  in  some  cases,  we  have  acquired  many  names  for  the  same 
geological  horizon.     This  multitude  of  synonyms  causes  confu- 
sion  for  the  student  and  the   investigator;  but  it  must   not  be 
complained  of.     The  synonymy,  for  the  greater  part,  affects  only 
the  subordinate   divisions   of  the  rocks   and  these  are  not  here 
introduced. 

(6)  The  Law  of  Priority,     Geologists  have  agreed,  in  prac- 
tice, not  only  that  the  most  suitable  names  for  formations  are 
geographical,  but  that  the  one  first  proposed  shall  be   accepted 
generally,  and  thus  become  a  standard  designation.     But  it  is 
not  allowable  to  take  an  old  name  which  has  been  employed  to 
embrace  a  certain  range  of  strata,  and  subsequently  employ  it  for 
a  wider  or  narrower  range,  as  is  sometimes  done  by  geologists  in 
their  use  of  the  terms  "  Nashville  Group  "and  "  Waverly  Group." 
Against   either  of  these,  as  a  designation  of  an  assemblage  of 


STRUCTURAL   GEOLOGY.  273 

strata  wider  or  narrower  than  that  originally  designated,  any 
name  later  proposed  would  hold  the  right  of  priority. 

4.    Table  of  Geological  Equivalents.    We  will  now 

arrange  in  a  Table,  the  complete  series  of  formations  with  their 
accepted  classification,  descending  to  the  divisions  called  "  peri- 
ods "  and  "  groups."  Then,  in  parallel  columns,  we  will  insert 
the  names  of  the  equivalent  formations  as  known  in  particular 
regions.  We  will  select  a  few  states  in  which  investigations 
began  at  early  periods,  or  were  carried  on  without  the  possibility 
of  certain  connection  with  older  studied  states.  To  these  will  be 
added  a  column  showing  the  principal  English  equivalents.  The 
places  left  blank  indicate  what  formations  are  wanting  in  the 
several  regions. 

REMARKS. — The  student  may  take  notice  as  follows:  1.  The 
subdivisions  of  the  Jurassic,  standing  in  the  column  of  Ameri- 
can Standards,  cannot  be  said  to  have  come,  as  yet,  into  general 
use.  2.  The  Catskill  Group  is  generally  ranged  under  the  Devo- 
nian. 3.  The  Waverly  or  Marshall  is  not  generally  placed  in  the 
horizon  of  the  Catskill.  For  other  remarks  see  Chapter  V. 


274 


GEOLOGICAL   STUDIES. 


American  Standard. 

Pennsylva- 
nia. 

Ohio. 

Michigan. 

CJENOZOIC. 

QUARTERNARY. 

22 

Recent. 
Champlain. 
Glacial. 

Recent. 
Champlain. 
Glacial. 

Recent. 
Lacustrine. 
Glacial. 

Recent. 
Lacustrine. 
Glacial. 

TERTIARY. 

21 

Equus  Beds.       i  ^ 
Loup  R.  Gr.        jn 

20 

Truckee.             ^  g 
White  R.             o  ° 

19 

Uinta.                     as 
Bridger.               ^  f 
Wahsatch.         ^^ 

MESOZOIC. 

CRETACEOUS. 

18 
17 

Laramie. 
Fox  Hills. 
Colorado. 
Dakota. 

JURASSIC. 

Flaming:  Gorge  Gr. 
White  Cliff  Gr. 

TRIASSIC. 

16 

Star  Peak  Gr. 
Koipato  Gr. 

Red  Sandstone. 

PALAEOZOIC. 

UPPER  CARBO 
NIFEROUS. 

LOWER  CARBO- 
NIFEROUS. 

15 

Permian. 

14b   Coal  Measures. 

XIII.  Coal  Meas. 

Coal  Meas. 

Coal  Meas. 

Ha 

Conglomerate. 

XII.    Serai. 

Homewood  8. 

Parma  Cong. 

13     Carbonif.  Lim. 

NEW  YORK.  

12    !CatskillGr. 

XI.       Umbral. 
X.         Vespertine. 
IX.       Poiient. 

Maxville  L. 
Waverly  Gr. 

Carbonif.  Lim. 
Mich.  Salt  Gr. 

Marshall  Gr. 

DEVONIAN. 

11    IChemungGr. 

VIII.  Vergent. 

Erie  Shale. 

Huron  Gr. 

10 
9 

Hamilton  Gr. 
Corniferous  Gr. 

VIII.  Cadent. 
VIII.  Post  MeridT" 

Huron  Shale. 
Hamilton  Gr. 
Corniferous. 

Little  Traverse. 
Mackinac  Gr. 

8     Oriskany  Gr. 

VII.     Meridian. 

Oriskany. 

SILURIAN. 
CAMBRIAN. 

7 
6 

Helderberg  Gr. 

VI.       Premeridian. 

Waterlime. 

Waterlime. 

Salina  Gr. 

VI.       Scalent. 

Salina. 

Salina. 

5     Niagara  Gr. 

V.        Surgent. 
IV.      Levant. 

Niagara. 

Niagara. 

4     Trenton  Gr. 

III.      Matinal. 

Trenton. 

Trenton. 

3     Canadian  Gr. 

II.        Auroral. 

(Underlying.) 

Canadian.     • 

2     Primordial  Gr. 

I.          Primal. 

(Underlying.) 

L.  Superior  S. 

62 

% 

HURONIAN. 

1 

Keweenian. 

Keweenian. 

Huronian. 

LAURENTIAN. 

Laurentian. 

STRUCTURAL    GEOLOGY. 


275 


Canada. 

Great  Britain. 

Europe. 

Miscellaneous. 

Recent. 
Leda    Clay    or    Erie 
Clay. 
Glacial. 

Recent. 
(  Pleistocene. 

Recent. 

Laterite.    (India.) 

Pliocene     or    English 
Crag. 

Pliocene  —  Sub  -  Apen- 
nine  ;  Antwerp  sands. 

—  Niobrara. 

Miocene. 

Miocene  —  Faluns     of 
Touraine;  Upper  Mo- 
lasse. 
Oligocene  —  Rupelian 

Eocene. 

and  Tongrian. 
Eocene  —  Londiniaii; 
Parisian  ;     N  u  m  m  u  - 
litic. 

I   Vicksburg. 
(   Claiborne.    Tejon,  Cal. 

tfPPe-.  !SVte' 
Middle,i 
/•  Green  Sand. 
Lower,  ) 

Danian. 
Senonian. 
Turonian. 
Cenomanian. 
Gault. 
Neocomian. 

1   Chico,        1 
•  (Hiatus)    leal. 
J   Shasta. 

Vealden. 
I  Upper, 
Oolite,  4  Middle, 
(  Lower. 

Lias. 

Portlandian. 
Oxfordian. 
Bathonian. 
Toarcian,        7  B1     k 
Liasian,           ,    T 
Sinemurian.  }    J' 

Atlantosaurus  Beds. 
Baptanodon  Beds. 

Rhaetic  Beds. 
Red  Marls. 
Shell  L. 
Variegated  S. 

Keuper. 
Muschelkalk. 
Bunter  Sandstein. 

Marnes  irises. 
Calcaire  coquillier. 
Gres  bigarre. 

Marl  Slate  and  L. 
Red  Sandstones. 

Flothliengendes. 

Dyas  (Europe). 

Coal  Meas. 

Coal  Meas. 

Terrain      h  o  u  i  1  1  e  r  — 
Steinkohlen  format. 

Upper. 
)  Lower  of  Rogers' 

Bonaventure  C. 

Millstone  Grit. 

Flotzleer  Sandstein. 

Lower,  > 
)  Conglom.  Meas. 

Mountain  L. 

Calcaire     Carbonifere; 
Kohlenkalk;  Kulm. 

Mauch  Chunk  Shale  (Pa.). 

Petherwin  Gr.               *> 
1 

Kinderhook    (111.);     Chou- 
teau  L.  (Mo.);    Yellow  S. 
(Iowa);       Silicious       Gr. 
(Tenn.),  part. 

Chemung.                  6 

Dartmouth  Gr.              * 

Hamilton. 

0(J5 

Plymouth  Gr.                £ 

Eifel  L. 

Corniferous.          ^tw 

2 

c  ° 
1 

Liskeard  Gr. 

Spirifer  S. 

Ludlow. 

Salina. 

Wenlock. 

Niagara. 

Upper  Llandovery. 

Trenton. 

Lower  Llandovery. 

Canadian. 

Caradoc  and  Bala. 
Llandeilo  Flags. 

Primordial. 

Arenig. 
Tremadoc  Slate. 
Cambrian. 

TT         (  Tremadoc  SI.     ~)      a 
up-      1  Lingula  Flags.  | 
CMenevian.           !>  ;,'c 
Low.  ^Harlech  and     |^ 
(     Longmynd.     J  u 

Keweenian. 

Huronian. 

Fundamental 

Laurentian. 

CHAPTER  III. 
DYNAMICAL  GEOLOGY; 

OB,    WHAT     HAS     BEEN     LEARNED    ABOUT    GEOLOGICAL    AGENCIES. 

WE  should  now  make  some  condensed  statements  respecting 
the  forces,  agencies,  and  methods  of  geological  work.  How  have 
these  physical  results  been  accomplished  to  which  our  attention 
has  thus  far  in  this  Part  been  turned  ?  How  have  rocks  origi- 
nated? How  have  they  been  consolidated?  How  upturned, 
folded,  and  plicated  ?  How  metamorphosed  ?  How  have  mount- 
ains been  uplifted,  valleys  sunken,  and  the  basins  of  the  lakes 
and  oceans  scooped  out  ?  The  explanation  of  these  phenomena 
belongs  to  Dynamical  Geology.  We  must  restrict  ourselves  to 
very  summary  statements. 

§  1.     Agency  of  Water. 

1.  Running  Water.  We  begin  with  the  action  of  run- 
ning water,  because  its  results  are  most  familiar.  The  mere  im- 
pact of  rain  drops  on  the  surface  disintegrates  the  soil  and  even 
the  solid  rocks.  The  dripping  from  the  roofs  of  caves  sometimes 
wears  flutings  in  the  stony  walls.  But  rain  water  accumulated  in 
torrents  works  sometimes  with  amazing  energy.  The  destructive 
wear  of  any  swollen  stream  is  something  which  has  attracted  the 
notice  of  all.  Most  of  the  erosive  work  in  sediment-bearing 
streams  is  by  corrasion. 

Every  modern  river  flows  in  a  valley,  and  the  valley  is  simply 
a  record  of  the  river's  erosive  work.  To  what  this  in  many  cases 
amounts  has  been  illustrated  in  Study  XVI  and  elsewhere. 

Where  a  stream  is  precipitated  over  a  "  fall,"  the  reaction  of 
the  water  at  the  foot  gradually  undermines  the  cliff,  and  it  breaks 
down  by  degrees.  This  is  more  rapid  than  ordinary  erosion. 

276 


DYNAMICAL   GEOLOGY. 


277 


Most  high  waterfalls  are  by  such  means  in  process  of  recession. 
As  the  recession  continues,  the  foot  of  the  fall  gradually  rises. 
Unless  a  fall,  therefore,  retreats  up  a  rapid  stream,  its  height 
must  continually  diminish,  and  at  last  the  fall  will  be  sloped  off 
to  a  rapid  chute. 

Subterranean  streams  erode  chiefly  by  solution  arid  by  friction 
of  the  water.  A  stream  flowing  through  a  fissure  constantly  en- 
larges it;  but  more  especially  if  the  fissure  is  in  limestone.  By 
such  means  caverns  have  been  produced,  some  of  which,  like  the 
Adelsberg  and  the  Mammoth  caverns,  have  become  wonders  of 
the  world.  The  latter  (Fig.  209)  has  many  winding  and  mutually 


FIG.  209.— PLAN  OF  MAMMOTH  CAVE.     (Hovey.) 

intersecting  passages,  which  aggregate  in  length  150  miles.  The 
diameter  of  the  area  covered  by  the  cavern  is  10  miles,  and  the 
main  passage  extends  4  miles.  It  is  from  40  to  300  feet  wide, 
and  from  35  to  125  feet  high. 

The  amount  of  sediment  transported  by  great  rivers  is  quite 
enormous.  According  to  the  investigations  of  Humphreys  and 
Abbot,  the  silt  carried  to  the  Gulf  of  Mexico  by  the  Mississippi 
River  amounts  to  l-1500th  the  weight  of  the  water,  or  l-2900th 


278  GEOLOGICAL   STUDIES. 

its  bulk.  This  silt  amounts,  in  other  words,  to  812,500,000,000,000 
pounds  per  year,  or  a  mass  1  mile  square  and  241  feet  deep. 
Besides  this,  the  Mississippi  pushes  along  to  the  gulf  an  addi- 
tional amount  of  mud,  which,  added  to  that  floated,  would  form  a 
mass  a  mile  square  and  268  feet  deep.  This  amount  removed  an- 
nually from  the  whole  basin  of  the  Mississippi  would  lower  it  1 
foot  in  4,920  years.  Other  great  rivers  accomplish  equal  or 
greater  results.  The  Ganges  lowers  its  basin  by  erosion  1  foot  in 
1,880  years. 

The  river  sediments  which  find  their  way  to  the  sea  are  widely 
dispersed  over  its  bottom.  The  finer  are  transported  to  greatest 
distances;  the  coarser  are  deposited  nearer  the  shore.  Between 
the  remote  distances  and  the  shore  all  grades  of  sediments  are 
laid  down.  If  the  sediments  have  such  density  as  to  sink  10 
feet  an  hour,  and  the  motion  of  the  water  is  2  miles  an  hour, 
then  the  sediment  would  float  200  miles  before  settling  1,000  feet. 
Sediments  of  less  fineness  would  float  less  distances.  But  while 
such  suspension  occurs  in  fresh  waters,  the  same  sediments  in 
salt  water  would  sink  in  l-15th  the  time.  Hence,  as  a  fact,  marine 
sediments  would  be  deposited  along  a  shore  belt  comparatively 
narrow,  did  not  the  agitation  of  the  water  near  the  surface  pro- 
long the  period  of  suspension  of  a  portion  of  the  sediments. 

River  sediments  also,  at  time  of  overflow,  are  more  or  less 
widely  spread  over  the  adjoining  flood  plain.  Thus  alluvial  de- 
posits are  formed,  which  fill  to  a  greater  or  less  extent  the  rock- 
bottomed  valley  occupied  by  the  river  (Fig.  210).  In  this  cut,// 


PIG.  210.— SECTION  ACROSS  A  TEKRACED  RIVER  VALLEY. 

is  the  level  of  the  alluvial  plain  at  a  certain  time.  If  subse- 
quently the  amount  of  water  diminishes,  dec'  becomes  the  level 
of  the  alluvial  plain.  By  a  further  diminution,  the  flood  plain  is 


DYKAMICAL   GEOLOGY.  279 

lowered  to  b  a  a'  b'.  These  steps  in  the  alluvial  slope  are  ter- 
races, due  to  different  stages  of  the  water.  Sometimes  two  ter- 
races occur  on  one  side  as  the  equivalent  of  a  single  one  on  the 
opposite  side. 

If,  after  a  river  has  become  established  in  its  rocky  bed,  a 
subsidence  takes  place,  sediment  will  accumulate  underneath  the 
channel,  and  the  river  will  flow  over  a  mud-formed  bed.  This 
has  occurred  with  the  river  whose  valley  section  is  shown  in  the 
diagram.  If  afterward  the  bottom  should  be  elevated,  the  mud 
would  be  scoured  out. 

The  bar  so  commonly  formed  across  the  mouths  of  great 
rivers  results  from  the  sediment  pushed  into  the  sea.  The  devel- 
opment of  the  bar  causes  the  extension  of  the  delta.  The  Mis- 
sissippi bar  advances  338  feet  annually  over  a  width  of  11,500 
feet,  and  the  delta  has  grown  into  a  deep  indentation  in  the  shore 
line  of  the  gulf.  The  whole  area  taken  by  the  delta^from  the 
gulf  is  12,300  square  miles.  This  illustrates  the  nature  of  the 
work  performed  by  the  great  rivers. 

2.  Oceanic  Action.  (1)  Ocean  Currents.  These  currents 
exert  important  agency  in  transporting  any  sediments  which  they 
float.  The  fine  floating  sediments  of  the  Mississippi  are  borne 
hundreds  of  miles,  and  even  to  the  Straits  of  Florida.  The  tur- 
bid water  of  the  Amazons  is  traceable  northward  a  very  great 
distance.  Generally  these  currents  flow  far  from  land,  and  con- 
tribute little  to  the  process  of  erosion. 

The  bottom  of  the  Atlantic,  along  the  Arctic  belt,  reaching 
southward  to  a  point  60  miles  beyond  Nantucket,  is  covered  by 
a  coarse  gravel  or  sand;  that  of  the  great  depths  by  a  sticky 
mud.  Under  the  Gulf  Stream  the  bottom  is  of  sand,  of  so  fine 
a  grain  that  the  grains  can  only  be  distinguished  under  a  micro- 
scope. Mixed  with  it  are  masses  of  minute  shells.  The  two 
form  a  bed  as  level  and  hard  as  a  floor.  Bowlders  are  occasion- 
ally found,  dropped,  probably,  from  cakes  of  ice  floating  from 
shore. 

(2)  Wave  Action.  The  waves  reach  the  shore  and  exert  a 
vast  mechanical  agency.  Not  only  is  the  power  great,  but  its 


280  GEOLOGICAL   STUDIES. 

exertion  is  incessant.  The  highest  waves  are  only  about  43 
feet  above  the  bottom  of  the  trough  between  them;  but  the 
force  with  which  they  sometimes  strike  a  solid  resistance  is  two 
or  three  tons  to  the  square  foot.  Such  force  —  or  even  the 
ordinary  wave  force  during  a  winter  (2,000  pounds  per  square 
foot)  —  exerted  on  an  ordinary  beach,  must  cause  its  rapid  disin- 
tegration. Accordingly  we  learn  that  whole  towns  have  been 
undermined,  and  many  solid  acres  distributed  over  the  ocean's 
bottom.  Tidal  Waves  along  shore  act  with  similar  energy.  In 
straits,  small  bays,  and  estuaries,  the  rise  of  the  tide  sometimes 
amounts  to  20,  30,  or  50  feet,  and  it  sweeps  along  with  destruc- 
tive force.  The  bore  of  the  Hoogley  (a  mouth  of  the  Ganges) 
and  the  piroroco  of  the  Amazons  are  famous.  In  the  Bay  of 
Fundy  the  rise  of  the  spring  tides  is  sometimes  60  feet.  Under 
the  action  of  the  waves,  large  continental  areas  have  in  times 
past  been  wasted;  straits  like  Behring  and  Gibraltar  have  been 
cut;  connections  of  land  and  water  have  been  modified;  climates 
have  been  changed,  faunas  and  floras  exterminated  and  replaced 
by  others.  Shore  action,  indeed,  has  been  largely  instrumental  in 
that  wastage  of  continental  masses  which  is  believed,  in  some 
cases,  to  have  resulted  in  their  total  disappearance. 

3.  Action  of  Ice.  The  freezing  of  water  held  in  the  pores 
of  rocks  and  minerals  is  a  very  powerful  disintegrating  agency. 
Fine  aluminous  limestones  just  from  the  quarry,  when  exposed 
to  the  action  of  a  winter's  frost,  split  into  many  pieces.  Sand- 
stones and  granites  crumble  to  sand.  Crevices  are  pried  asunder, 
and  the  most  stubborn  quartzites  are  slowly  reduced  to  frag- 
ments. 

Floating  Ice  in  rivers  acts  as  an  efficient  agent  of  corrasion. 
It  carries  also,  in  some  cases,  large  volumes  of  sediment,  and  dis- 
tributes seeds  along  the  valley  of  the  stream. 

In  the  form  of  Glaciers,  ice  seems  to  have  performed  impor- 
tant work  in  ages  past;  and  our  small  modern  glaciers  probably 
typify  the  modes  of  action  of  the  ancient  ones.  A  Glacier  is  a 
sheet  of  ice  resting  in  a  mountain  valley.  It  resulted  from  accu- 
mulations of  snow  for  years,  unmelted  by  the  summer's  warmth. 


DYNAMICAL    GEOLOGY. 


281 


The  glacier  stretches  upward  into  the  region  of  perpetual  snow. 
Fig.  211  is  a  view  of  a  couple  of  modern  Alpine  glaciers,  des 
Bossons  at  the  left  and  Tacconnay  on  the  right,  with  Mont  Blanc, 
the  highest  summit,  in  the  centre.  The  glacier  moves  continually 
downward,  and  would  encroach  on  the  cultivated  fields  if  the  ice 
were  not  melted  away  at  the  foot.  The  Glacier  des  Bossons 
transported  the  bodies  of  the  victims  of  an  avalanche  27,500  feet 
in  forty-one  years,  or  about  670  feet  a  year.  The  Great  Glacier 


FIG.  211.— VIEW  OF  THE  GLACIER  DES  BOSSONS  AND  MONT  BLANC,  FROM  THE  BREVENT, 

8,000  FEET  HIGH. 

of  Alaska  moves  a  quarter  of  a  mile  per  annum,  or  twice  as 
rapidly  as  Bossons.  Many  rocky  fragments  roll  down  on  the 
glacier  from  the  adjoining  slopes.  These,  at  last,  are  landed  at 
the  foot  of  the  glacier,  and  there  accumulate  a  terminal  moraine, 
which  is  shown  in  the  figure.  A  lateral  moraine  is  accumulated, 
also,  along  each  border.  These  unstratified  accumulations  of 
worn  and  rounded  stones  remind  us  of  the  bowlders  in  the  ordi- 
nary Drift;  and  these  moraines  look  like  some  of  the  Drift  hills 


282 


GEOLOGICAL   STUDIES. 


scattered  over  our  Northern  States.  (Fig.  5.)  The  Alpine  mo- 
raines, however,  are  destitute  of  all  traces  of  stratification. 
(Fig.  212.) 

Moreover,  these  glaciers  by  their  motion  leave  scratches  on 
the  underlying  rocky  surfaces  identical  in  appearance  with  those 
found  on  the  bed  rock  throughout  the  Northern  States.  One  of 
the  anciently  striated  surfaces  is  shown  in  the  adjoining  cut,  Fig. 
213.  This  shows  that  the  most  flinty  materials  have  yielded  to 
the  action  which  has  grooved  the  ancient  rock  surfaces. 

The  surface  of  Greenland  is  completely  covered  by  a  modern 
glacier.  A  little  depression  of  the  summer  temperature  would 


FIG.  212.— TERMINAL  MORAINE  AND  BOWLDER-STREWN  AREA  AT  THE  FOOT  OP  THE 
MER  DE  GLACE.    Compare  the  Bowlder- Covered  Areas  in  Figs.  6  and  37. 

extend  the  glaciated  surface  over  part  of  North  America.  It  is 
quite  conceivable  that  without  any  great  severity  of  cold,  an  ice 
covering  might  become  permanent  as  far  south  as  Chicago  and 
Cleveland. 

Glaciers  exert  powerful  erosive  action  through  the  instrumen- 
tality of  the  sand  and  pebbles  frozen  into  the  bottom  or  pressed 
between  the  ice  and  the  rock.  Where  the  glacier  is  1,000  feet 
thick,  its  pressure  on  the  underlying  rock  is  4,870  pounds  to  the 
square  foot.  Corroborative  evidence  of  the  great  grinding  effi- 
ciency of  glaciers  is  furnished  by  the  stream  of  densely  turbid 


DYNAMICAL   GEOLOGY. 


283 


water  which  issues  at  the  foot.  The  stream  which  drains  the  Aar 
glacier  brings  down  280  tons  per  day,  and  the  Justedal  glacier  of 
Norway  wears  down  60,000  cubic  metres  of  rock  annually. 

A  glacier  mass  reaching  the  sea,  protrudes  into  it,  is  buoyed 
up  by  it,  and  finally  broken  off.  The  detached  fragment  then 
floats  away  as  an  iceberg,  bearing  with  it  mud  and  other  debris 
from  its  northern  home.  The  icebergs  in  the  North  Atlantic 
originate  on  the  west  coast  of  Greenland. 


FIG.  213.— A  STRIATED  DOME  OF  QUARTZITE,  FRAZER  BAY,  LAKE  HURON. 
(Dr.  E.  Andrews.) 

4.  Assortment  of  Marine  Sediments.  Water  and  ice 
are  thus  agents  for  the  creation  and  transportation  of  sediments, 
and  their  delivery  in  the  sea.  Borne  by  tides  and  currents,  their 
unequal  rates  of  deposition  result  in  a  complete  assortment  of  the 
materials.  At  all  times  the  sediment  is  coarser  near  the  shore, 
and  grows  finer  with  distance.  On  this  point  Darwin  has  fur- 
nished some  specific  data,  obtained  between  Santa  Cruz  and  the 
Falkland  Islands,  on  gradation  in  size  of  transported  materials. 
These  are  cited  below: 


284  GEOLOGICAL   STUDIES. 

Miles  from  Depth  in 

Shore.  Fathoms.  Coarseness  of  Materials. 

2  to  4  ..  11  to  12  ...  Pebbles  size  of  walnuts  and  smaller. 

4  to  7  ..  17  to  19  ...  Do.  size  of  hazel  nuts. 

10  to  11  ..  23  to  25  ...  .3  to  .4  inch  in  diameter. 

12  ..  30  to  40  ...  .2  inch  in  diameter. 

22  to  150  .      .  45  to  65  .     .      .  .1  inch  in  diameter  to  fine  sand. 

At  any  point,  however,  the  coarseness  of  the  deposit  depends 
on  the  rate  of  movement  of  the  water.  Should  any  cause  increase 
at  any  place  the  transporting  power  of  the  water,  coarser  sedi- 
ments would  be  dropped  at  this  place,  and  the  finer  would  be 
carried  beyond.  So  the  same  spot  would  receive  a  graduated 
succession  of  sedimentary  sheets.  We  should  have  there,  in 
such  case,  a  real  cycle  of  sedimentation.  This  would  be  repeated 
as  many  times  as  the  range  of  variation  in  the  transporting  power 
of  the  water  should  be  repeated.  Hence,  probably,  the  cycle  in 
the  succession  of  rocky  strata  described  on  page  268. 

§  3.     Agency  of  the  Atmosphere. 

1.  Wear  by  Wind-borne  Sands.  The  only  atmos- 
pheric action  important  to  consider  here  is  its  transportation  of 
sands.  Incidental  to  the  movement  of  blown  sands  is  the  polish- 
ing and  wearing  which  result  from  the  impinging  of  the  sand 
particles  against  hard  surfaces.  Quartzose  bowlders,  and  still 
more  other  rocks,  become  polished  all  over  their  exposed  sides, 
the  actions  extending  equally  to  the  bottoms  of  the  depressions 
in  the  originally  irregular  surface.  This  effect  is  well  observed 
along  the  sand-covered  eastern  border  of  Lake  Michigan,  and 
particularly  on  the  sand-strewn  plateau  slope  stretching  eastward 
from  Sleeping  Bear  in  Leelanau  county.  In  the  pass  of  San  Ber- 
nardino, California,  the  granite  is  scratched  like  a  glaciated  sur- 
face (W.  P.  Blake).  Very  marked  effects  have  been  reported 
from  the  Gila,  Amargosa,  and  Colorado  deserts  by  Newberry  and 
Gilbert.  On  Cape  Cod  the  driven  sands  even  grind  quite  through 
the  window  panes.  In  the  arts,  steam-driven  sand  is  employed  in 
etching  and  carving. 


DYNAMICAL   GEOLOGY.  285 

2.  Sand  Dunes.  These  are  banks  or  hills  of  dry  sand 
piled  up  by  the  wind.  In  the  temperate  zone  the  prevailing 
direction  of  the  wind  is  westerly;  hence  the  drifted  sands  have  a 
resultant  eastward  movement,  and  thus  they  continue  to  travel, 
burying  lands  and  houses  and  highways  in  their  course.  Along 
the  eastern  shores  of  our  inland  lakes,  the  sand  which  is  thrown 
up  by  the  waves  is  an  exhaustless  source.  When  dried,  the  wind 
drives  it  inland,  forming  banks  and  hills  thirty  to  over  a  hundred 
feet  high.  At  New  Buffalo,  on  the  eastern  shore  of  Lake  Michi- 
gan, the  dunes  measure  93  feet  in  height,  and  at  Grand  Haven 
they  are  215  feet  on  the  north  side  of  Grand  River  and  205 
feet  on  the  south  side.  The  track  and  station  buildings  of  the 
Detroit  and  Milwaukee  Railway,  originally  built  on  the  north 
side,  were  so  persistently  encroached  on  by  the  sands  that  they 
were  removed  to  the  opposite  side.  At  Sleeping  Bear,  the  sands 
are  drifting  over  a  promontory  500  feet  high.  From  the  summit 
a  wide  waste  of  sand  spreads  over  several  square  miles.  Here 
and  at  Grand  Haven,  the  singular  spectacle  is  presented  of  a 
dead  forest  protruding  its  tree  tops  a  few  feet  above  the  surface 
of  the  deluge  of  sand. 

The  dunes  of  England  and  the  northern  coasts  of  France, 
Denmark,  and  Russia  have,  in  past  times,  made  serious  encroach- 
ments on  human  improvements.  They  have  been  the  study  of 
agriculturists  and  of  scientific  commissions,  and  at  present  a 
large  degree  of  control  is  exercised  over  them. 

We  see  no  limit  to  the  amount  of  sand  which  might  thus  be 
drifted,  nor  to  the  distance  over  which  it  might  travel.  Von 
Richthofen  maintains  that  the  great  loess  deposits  of  China  are 
mere  beds  of  fine  sand  blown  perhaps  from  the  Mongolian  desert; 
and  Pumpelly  inclines  to  accept  a  similar  origin  for  the  similar 
loess  beds  of  the  valleys  of  the  Mississippi,  Missouri,  Des  Moines, 
and  other  rivers.  Others,  however,  think  them  of  fluviatile 
origin.  If  of  reolian,  or  wind-borne,  origin,  some  adequate 
source  of  supply  must  be  pointed  out.  King  has  suggested  that 
this  may  have  been  in  the  arid  regions  of  the  Cordilleras,  where 
trains  of  dunes  are  still  moving  eastward,  and  must  have  moved 


286  GEOLOGICAL   STUDIES. 

in  much  greater  abundance  during  the  secular  dry  period  of  the 
Quaternary  Age. 

3.  Transportation  of  Volcanic  Ashes.  The  atmos- 
phere exerts  a  similar  agency  in  the  transportation  of  volcanic 
"  ashes,"  as  already  stated  in  connection  with  the  phenomena  of 
volcanoes  (See  Study  XXIII).  Dust  from  other  sources,  and 
even  dust  probably  of  cosmic  origin,  appears  to  be  borne  and 
sustained  in  the  atmosphere  almost  indefinitely,  destined  at  last 
to  be  brought  down  by  precipitations  of  rain  and  snow.  We 
present  here  grains  of  magnetic  iron  appearing  to  have  been 
fused — probably  the  dust  of  a  volatilized  meteor. 


FIGS.  214,  215,  216.— CORPUSCLES  OF  MAGNETIC  IRON  BELIEVED  TO  BE  or  COSMIC  ORIGIN. 
X  500.    (Tissandier.) 

214— From  the  enow  of  Mont  Blanc  at  the  height  of  2710  metres. 
215— Collected  from  rain  water  at  Sainte  Marie  du  Mont. 
216— From  the  dust  collected  in  the  unfrequented  towers  of  Notre  Dame,  Paris. 

§  3.     Agency  of  Heat. 

In  Studies  XXII,  XXIII,  and  XXIV  numerous  geological 
facts  have  been  brought  to  view  which  point  to  the  agency  of 
heat.  The  phenomena  of  thermal  springs,  volcanoes,  and  ancient 
lavas  are  most  naturally  explained  on  the  theory  of  a  high  inter- 
nal temperature.  The  actual  increase  of  heat  experienced  as  we 
penetrate  the  earth  is  direct  evidence  that  a  high  temperature 
prevails  generally  within  one  or  two  hundred  miles  of  the  earth's 


DYNAMICAL   GEOLOGY.  287 

surface.  As  this  interior  heat  is  constantly  escaping,  there  either 
must  be  some  existing  source  of  supply,  or  else,  in  ages  past,  we 
have  ground  to  argue,  a  much  higher  temperature  has  existed 
within,  and  consequently  has  transmitted  a  much  higher  degree 
of  thermal  energy  to  the  terrestrial  surface.  Probably  both 
alternatives  represent  the  facts. 

If  the  earth  is  conceived  as  a  cooling  body,  we  must  seek  for 
the  records  of  the  action  of  heat  at  a  former  high  temperature. 
These  records  would  reveal  (1)  The  consequences  of  the  direct 
action  of  heat,  and  (2)  The  consequences  of  the  slow  abatement 
of  the  heat  —  especially  the  contraction  incident  to  cooling. 

1.  Geological  Results  of  Former  High  Tempera- 
ture. (1.)  A  Primitive  Molten  State.  If  the  primitive  tem- 
perature of  the  earth  was  such  as  to  reduce  the  entire  globe  to  a 
state  of  fusion,  then  there  was  at  some  time  a  first  crust — a  fire- 
formed  crust.  On  this  the  stratified  sediments  must  eventually 
have  accumulated.  Later  sediments  we  know  accumulated  in 
later  ages,  until  we  have  in  modern  times  a  measured  thickness 
of  more  than  a  hundred  thousand  feet  of  solid  rocks.  But 
these,  according  to  modern  views,  are  all  of  sedimentary  origin, 
e*xcept  an  insignificant  amount  of  erupted  and  intrusive  rocks. 
What  has  become  of  the  fire-formed  crust  ?  Can  we  expect  ever 
to  uncover  it  or  penetrate  to  it  as  a  fact  of  observation  ?  We 
are  persuaded  it  has  long  since  disappeared. 

If  ocean  sediments  accumulated  on  the  fire-formed  crust,  the 
first  effect  was  to  thicken  the  envelope  within  which  the  earth's 
internal  heat  was  imprisoned.  The  previous  thickness  of  the 
(fire-formed)  crust  was  such  as  was  demanded  by  the  internal 
temperature  and  the  thermal  conducting  power  of  the  materials. 
With  the  sediments  added,  there  was  an  excess  of  thickness,  and 
the  heat  within  would  re-fuse  the  under  layer  of  the  igneous 
crust.  So,  much  of  it  would  disappear.  The  addition  of  further 
sediments  would  cause  the  loss  of  further  portions  from  the  under 
surface.  This  process  would  continue.  At  length  the  entire 
igneous  crust  would  have  disappeared,  the  molten  central  mass 
becoming  inclosed  by  rocks  which  had  been  sea  sediments.  Nor 


288  GEOLOGICAL   STUDIES. 

is  this  the  end.  The  process  of  eating  away  from  the  under  side 
would  continue  even  to  the  disappearance  of  the  older  portions 
of  the  sedimentary  crust.  How  much  of  the  sedimentary  crust 
may  thus  have  disappeared  it  is  impossible  to  ascertain.  The 
lowest  strata  ever  observed  are  probably  in  position  far  above  the 
oldest  ever  formed.  We  are  quite  at  liberty  to  assume  any  such 
disappearance  of  oldest  formed  strata  as  facts  of  observation  may 
suggest. 


FIG,  217. — ASCENT  OF  ISOGEOTHERMAL  PLANES  IN  THE  EARTH'S  CRUST. 

The  process  of  subterfusion  of  primitive  portions  of  the  crust 
is  otherwise  expressed  as  an  ascent  of  the  isogeothermal  planes  — 
the  planes  of  equal  temperature  within  the  crust.  The  process  is 
graphically  illustrated  by  Fig.  217.  The  line  c  c'  represents  the 
bottom  of  the  sea,  on  which  sediments  are  accumulating.  Evi- 
dences existing,  to  which  reference  will  be  made,  that  a  load  of 
sediments  causes  subsidence  of  the  bottom,  we  may  for  con- 
venience assume  that  the  subsidence  equals  the  filling,  and  the 
line  c  c'  remains  fixed.  Then  let  c  r,  or  c'  r' ,  represent  the 


DYNAMICAL    GEOLOGY.  289 

constant  thickness  determined  by  the  thermal  conductivity  of  the 
crust  materials.  A,  on  the  left,  represents  a  section  of  the  fire- 
formed  crust,  and  M,  a  portion  of  the  underlying  molten  matter. 
Then,  as  the  successive  additions,  B,  C,  D,  of  sedimentary  matter 
are  made,  successive  portions  A',  A',  of  the  fire-formed  crust  will 
be  melted  off.  The  total  re-fused  at  successive  intervals  is  shown 
at  A',  A',  A' ;  while,  in  the  last  case,  a  portion,  B',  of  the  sedi- 
mentary bed  B  has  also  disappeared. 

It  will  be  vain,  therefore,  to  expect  to  see  any  of  the  primitive 
earth  crust.  It  is  equally  vain  to  pretend  that  its  non-discovery 
is  any  proof  of  its  non-existence  at  the  beginning1  of  incrustation. 

(2)  Origin  of  Erupted  Material.     With  this  conception  of 
a  molten  interior,  it  is  easy  to  understand  the  origin  of  ancient 
or    modern    molten    matter.       In    another    connection    we    shall 
endeavor  to  point  out  the  causes  of  its  ascent  to  the  surface.     It 
seems  probable,  also,  that  the  frequency  of  the  outflows  would 
be  greatest  in  early  times,  when  the  crust  was  thinnest,  and  the 
progress  of  cooling  most  rapid. 

(3)  Agency  of  Steam  in  Eruptive  Action.     Some  force  act- 
ing upward  with  great  energy  reveals  its  existence  in  the  eruption 
of  thermal  waters  and  volcanic  ejecta.     While  steam  may  exert 
the   eruptive   force   in   the   case  of  geysers,  and  to  a  collateral 
extent  in  volcanoes,  there  are  reasons  for  believing  that  steam  is 
not  an  adequate   explanation  of  volcanic  or  seismic  action.     The 
presence  of  water  beneath  volcanoes  is  evinced  not  only  by  the 
usual  abundance  of  steam,  and  the  occasional  volumes  of  mud 
thrown  out,  but  also  by  the  escape  of  the  various  constituents  of 
sea  water,   such   as   chlorine,  sulphurous  acid,  sulphur,  common 
salt,   iodine,   and  bromine.       Some    connection  with   the   sea    is 
implied,  also,  in  the  arrangement  of  lines  of  volcanic  vents  around 
the  shores  of  the  continents.     The  percolation  of  water  to  the 
deep,   heated    interior   would    produce    results    which    are   quite 
intelligible;  and  it  is  quite  probable  that  some  eruptions  originate 
in  this  way.     But  the  copious  fissure  outflows  of  geologic  times 
must  be  otherwise  explained. 

(4)  Metamorphism.     During  the  ascent  of  the  lower  isogeo- 


290  GEOLOGICAL   STUDIES. 

thermal  planes  into  and  through  the  sedimentary  beds,  as  above 
explained,  the  latter  were  subjected  to  the  intense  action  of  heat. 
This  action  grew  more  and  more  intense  in  any  particular  one  of 
the  older  beds,  until  it  was  reached  by  the  plane  of  fusing  tem- 
perature, when,  of  course,  it  became  merged  in  the  general 
molten  mass.  With  the  heat  was  also  all  the  water  which  could 
percolate  through  the  rocks.  If,  at  a  sufficient  depth,  the  water 
was  converted  to  steam,  and  driven  toward  the  surface,  it  must 
be  remembered  that  deep-seated  water  was  subjected  to  enor- 
mous pressure,  and  retained  its  fluid  state  to  a  temperature  far 
above  212°  Fahr.  Without  doubt,  much  of  the  water  saturating 
the  deep  rocks  had  a  temperature  of  300°  to  800°.  Here,  then, 
were  the  conditions  of  intense  chemical  action,  and  of  other 
important  molecular  changes.  The  experiments  of  Daubree  and 
others  show  that  under  such  conditions  rocks  become  softened 
and  plastic,  the  molecules  of  matter  enter  into  new  arrangements, 
and  out  of  the  same  stuff  very  different  minerals  and  rock  masses 
come  into  existence.  Thus,  earthy  shales  become  slates,  or  even 
mica-schists;  limestones  become  marbles.  The  lines  of  sedimen- 
tation become  obliterated,  and  traces  of  fossils  disappear.  This 
result,  in  the  aggregate,  is  metamorphism. 

Its  progress  may  be  traced  in  the  changes  of  the  mineral  con- 
stituents of  the  rock.  The  molecules  which,  for  instance,  were 
so  arranged  as  to  constitute  a  crystal  of  augite,  rearrange  them- 
selves so  as  to  form  the  mineral  hornblende.  The  place  of  the 
old  crystal  remains  —  a  mould,  having  the  crystalline  form  of 
augite  —  but  the  mould  is  now  filled  with  a  substance  which,  if 
free  to  crystallize  by  itself,  would  not  take  the  form  in  which  it 
has  become  moulded.  It  is  a  pseudomorph.  It  has  the  substance 
of  one  mineral,  and  the  form  of  another.  This  hornblende  is  a 
pseudomorph  after  augite.  In  a  similar  way,  pyroxene  is  some- 
times altered  to  talc.  So,  also,  the  anhydrous  magnesian  sili- 
cates, chrysolite,  pyroxene,  and  chondrodite,  have  been  freqently 
found  changed  to  the  hydrous  magnesian  silicate,  serpentine. 
Other  cases  are  well  known.  When  the  pseudomorphism  of  the 
constituents  of  a  rock  involves  the  chief  mass,  so  that  the  rock 


DYNAMICAL    GEOLOGY.  291 

itself  is  altered,  the  change  is  known  as  pseudomorphic  meta- 
morphism,  or  metasomatism.  Serpentine  rock  and  the  talcitic 
rock  rensselagrite  are  examples. 

Regional  Metamorphism  is  that  which  takes  place  over  a 
wide  area  under  some  general  terrestrial  influence  as  just  ex- 
plained. Local  Metamorphism  is  caused  by  the  heat  accompa- 
nying the  eruption  of  molten  material  through  a  fissure.  The 
immediate  neighborhood  of  a  dike  is  generally  metamorphosed. 

(5)  The  Filling  of  Veins.  The  filling  of  true  banded  mineral 
veins  probably  depends  on  the  action  of  heat  and  water.  These 
are  powerful  agents  of  solution.  When  such  solutions  find  their 
way  into  the  cooler  parts  of  a  fissure,  precipitation  begins. 
Layer  after  layer  is  deposited,  probably  at  secular  intervals,  on 
the  fissure  walls.  The  nature  of  the  deposit  must  vary  with  the 
nature  of  the  solution  and  this  will  vary  with  the  source  from 
which  the  solution  proceeds.  When  precipitation  takes  place 
it  will  form  simultaneously  on  the  two  walls  of  the  fissure; 
hence  the  symmetry  of  the  arrangement  (see  Figs.  99  and 
100).  Possibly  some  veins  are  filled  by  a  process  of  sublima- 
tion, under  the  action  of  dry  heat.  Many  dikes  are  undoubt- 
edly filled  with  matter  in  a  state  of  fusion.  But  it  is  worth  while 
to  remember  that  the  action  of  heat  and  water  must  reduce  the 
deep-seated  rocks  on  a  large  scale  to  a  plastic  condition,  and 
that  such  rocks  are  necessarily  subjected  to  enormous  pressure. 
If,  then,  a  fissure  is  opened  to  them  or  through  them,  such  plastic 
substances  must  be  squeezed  in.  Thus,  apparently,  many  granite 
veins  have  originated,  and  perhaps  also,  some  porphyritic  and 
dioritic  veins.  An  injected  material  has  not  therefore,  of  neces- 
sity, a  molten  origin. 

2.  Effects  of  the  Earth's  Cooling.  (1)  Lateral  Pressure. 
Heretofore  in  considering  the  phenomena  of  mountains,  Studies 
XXV  and  XXVI,  we  have  discovered  convincing  proofs  of  the 
exertion  of  some  great  lateral  pressure.  On  the  theory  of  a  cool- 
ing and  contracting  globe,  we  find  an  explanation  of  lateral  press- 
ure which,  by  the  majority  of  geologists,  is  held  to  be  the  cause 
of  crustal  wrinkling  and  mountain  development.  It  is,  however, 


292  GEOLOGICAL   STUDIES. 

often  objected  that  the  whole  possible  shrinkage  in  the  circum- 
ference of  the  earth  due  to  cooling  from  the  temperature  of  first 
sedimentation  to  the  present,  would  not  be  sufficient  to  yield  the 
surplusage  worked  into  the  folds  and  plications  which  now  exist 
in  the  crust.  This  objection  acquires  weight  from  the  calcula- 
tions of  Fisher  and  Button,  and  from  the  studies  of  Claypole  on 
the  considerable  amount  of  shortening  supposed  to  have  taken 
place  in  a  section  through  the  Appalachians.  But  it  is  certain 
that  cooling  and  consequent  shrinkage  must  have  developed 
enormous  lateral  pressure,  and  it  is  eminently  probable  that  this 
pressure  found  relief  in  wrinkles  and  plications.  If  the  amount 
of  surplusage  afforded  by  this  means  is  insufficient,  we  shall 
presently  cite  another  source  of  surplusage  which  may  adequately 
supplement  this  one. 

(2)  Evolution  of  Heat.     Enormous  lateral  pressure  resulting 
from  the  earth's  contraction  would  necessarily  produce  more  or 
less  motion  ofr  the  parts  of  the  crust.     The  motion  would  be  ac- 
companied by  friction,  and  this  would  evolve  very  considerable 
amounts  of  heat.      Mallet  has  shown  that  the  crushing  of  small 
cubes  of  various  kinds  of  rocks  may  be  made  to  raise  the  temper- 
ature to  the  melting  point.     Much  more  would  the  crushing  press- 
ure resulting  from  the   earth's   contraction.       Mallet  and  others 
have  conceived  that  the  chief  part  of  the  earth's  internal  heat 
may  have  a  mechanical  origin.      This  suggestion  implies  the  non- 
existence  of  a  molten  core,  and,  in  fact,  the  diminution  of  heat 
toward  the  centre.     But  we  think  that  while  the  crushing  action 
would  develop  much  heat,  this  cause  is  not  adequate  to  produce 
results  on  such  a  scale  as  the  facts  of  geology  seem   to  require. 
The   whole   earth   has  moved  forward   in  all   its    continental  re- 
gions with  a   harmonious   and  synchronous  development.     This 
would  not  be  unless   all  parts  were   in   physical    sympathy  with 
each  other;  and  we  cannot  well  conceive  a  more  probable  way  in 
which  such  sympathy  could  exist  than  through  a  state  of  general 
plasticity  or  fusion. 

(3)  Seismic  Results  of  Contraction.     Different  parts  of  the 
earth's  crust  must  be  conceived  as  possessing  different  degrees  of 


DYNAMICAL   GEOLOGY.  293 

strength  and  rigidity.  This  would  result  from  different  rock- 
materials,  mixed  in  different  proportions,  differently  metamor- 
phosed, and  eventually  resting  in  different  positions.  A  strain, 
therefore,  under  which  one  part  would  yield,  would  be  resisted 
by  another  part.  The  stress  would  be  accumulated  in  the  most 
'rigid  parts.  But  no  rigidity  and  no  materials  could  resist  all 
stresses  resulting  from  the  action  of  the  earth's  mass.  Every 
part  must  finally  yield.  In  proportion  as  the  stress  was  great,  the 
final  shock  must  be  great.  The  shock  is  an  earthquake  move- 
ment. It  transmits  a  tremor  or  vibration  through  the  crust,  and 
this  may  be  felt  to  a  great  distance  from  the  seat  of  the  main 
collapse.  The  frequent  earthquake  tremors,  therefore,  are  in 
part,  merely  the  incidents  of  the  slow  contraction  of  the  earth. 

(4)  Mountain  Making.  The  principal  phenomena  of  moun- 
tains which  theory  must  seek  to  explain  are  as  follows:  (a)  The 
elevation;  (b)  the  folding  and  plication  of  the  strata;  (c)  the 
faulting;  (d)  the  accompanying  heat  and  metamorphism;  (e)  the 
great  thickening  of  the  mountain  strata;  (./*)  the  more  fragmen- 
tal  character  of  the  strata;  (g)  the  ekmgation  of  the  mountain 
uplift;  (A)  the  direction  of  the  elongation. 

Much  study  has  been  bestowed  on  the  explanation  of  these 
phenomena,  and  some  principles  have  been  generally  agreed  upon 
which  we  will  here  concisely  state. 

There  must  have  been  always,  since  the  ocean  existed,  a  sys- 
tem of  ocean  currents.  There  must  also  have  been  mineral  material 
held  in  suspension  in  the  sea  water  and  moved  along  with  the 
currents.  There  must  also  have  been  coarser  materials  rolled  and 
pushed  along.  Some  of  this  matter  was  simply  of  chemical  pre- 
cipitation; some  resulted  from  disintegration  of  shells  and  corals; 
but  the  most  bulky  part  was  detrital.  As  soon  as  the  conti- 
nental masses  rose  within  reach  of  the  action  of  the  waves  and 
currents,  mechanical  sediments  existed,  and  these  were  trans- 
ported by  the  currents.  The  currents,  while  originating  in  astro- 
nomical causes,  were  greatly  deflected  and  controlled  by  con- 
tinental shores,  and  even  by  continental  masses  while  yet  in  the 
germ  beneath  sea  level.  Supplies  of  detrital  material  there- 


294  GEOLOGICAL   STUDIES. 

fore,  furnished  from  any  source,  might  be  moved  —  partly  by  flo- 
tation and  partly  by  rolling  and  pushing  —  for  great  distances 
along  the  line  of  an  ocean  current.  In  the  course  of  ages,  the 
accumulation  of  sediment  along  this  line  would  so  load  the  sea 
bottom  that  subsidence  would  result.  The  accumulation  pro- 
ceeded step  by  step  with  the  subsidence.  Sediments  were  accu- 
mulating on  other  parts  of  the  sea  bottom,  but  not  so  copiously, 
nor  in  so  coarsely  fragmental  a  condition;  for  elsewhere  the 
transporting  power  of  the  water  was  less. 

The  downward  protrusion  of  the  sinking  sea  bottom  exposed 
the  deepest  portion  to  the  fusing  and  metamorphic  action  of  the 
internal  heat.  The  semifusion  and  softening  of  the  deeper  por- 
tion, and  perhaps  the  comparative  freshness  and  unsolidity  of  the 
upper  portion  made  the  line  of  subsidence  a  belt  of  weakness. 
We  are  not  in  this  connection  to  conceive  any  actual  consider- 
able downward  protrusion  along  the  sinking  region.  The  prog- 
ress was  slow.  The  protruding  portion  was  progressively  melted 
off.  A  nearly  uniform  thickness  of  the  crust  was  maintained, 
though  along  this  synclinal  the  exceptional  condition  of  the  ma- 
terials developed  exceptional  lack  of  rigidity. 

Accordingly,  when  in  the  progress  of  contraction,  accumulated 
strains  became  too  great  for  the  crust  to  withstand,  the  yielding, 
the  disturbance,  the  upfolding  would  take  place  along  the  enfee- 
bled synclinal — synclinal  in  its  texture  more  than  in  its  form. 
Here  a  fold  would  rise.  Here  a  mashing  together  of  the  softened 
materials  would  take  place.  Here  the  lateral  pressure  would 
most  plicate  the  plastic  sheets  of  sediments.  Here,  in  this  belt 
of  weakness,  would  be  developed  the  motion  due  to  the  contrac- 
tion that  had  taken  place  over  broad  areas  on  either  side.  Here 
the  sea  water  would  find  freest  access,  and  here  the  heat,  most 
readily  transmitted  from  below,  and  most  abundantly  generated 
by  most  extensive  motion,  would  work  most  extensive  meta- 
morphism. 

Thus  a  great  synclinal  fold  became  mashed  together  and  up- 
lifted into  an  anticlinal  mountain  elevation.  This  was  the  com- 
pletion of  a  synclinorium  —  a  mountain  system  originating  in  a 


DYNAMICAL   GEOLOGY.  295 

submarine  synclinal.  During  the  severe  ordeal  great  fractures 
must  have  resulted,  and  great  faultings  must  frequently  have 
been  produced.  We  have,  then,  in  this  account,  an  explanation 
which  covers  all  the  demands  of  mountain  phenomena,  except  the 
linear  forms  and  the  direction  of  the  trend;  and  these  we  think 
due  to  other  causes,  to  be  mentioned  in  another  section. 

The  weight  of  the  uplifted  synclinorium  exerted  on  each  side 
an  extraordinary  lateral  pressure.  There  existed,  consequently, 
a  tendency  to  the  uprise  of  other  ridges  parallel  with  the  first. 
When,  in  a  later  age,  the  crust  must  yield  again,  one  or  more 
broad  but  lower  folds  would  rise  alongside  of  the  primitive  uplift. 
Thus,  from  the  central  and  highest  crest  to  the  remotest  parallel 
fold  on  either  side,  and  the  plains  beyond,  a  general  descent  in 
the  extension  of  the  strata  constitutes  a  geanticlinal ;  and  the 
meeting  of  two  geanticlinal  slopes  in  the  broad  valley  between 
two  mountain  systems  forms  a  geosynclinal.  Mountain  folds 
thus  raised  are  destined  to  be  materially  lowered  in  altitude  and 
changed  in  contour  by  the  erosions  of  subsequent  periods. 

§  5.     Geological  Climates. 

1.  Terrestrial  Causes.  (1)  Greater  Heat  and  Greater 
Uniformity  of  Primitive  Climates.  The  progressive  cooling  of 
the  earth  has  resulted,  necessarily,  in  a  progressive  subsidence  of 
the  surface  temperature.  Heat  from  the  sun  and  heat  from  be- 
neath the  crust  are  two  chief  factors  in  terrestrial  climates.  The 
solar  heat  at  any  point  varies  with  the  inclination  of  the  solar 
rays.  The  influence  of  internal  heat  is  the  same  in  all  latitudes 
arid  at  all  seasons.  When  the  crust  was  thinner  this  influence 
was  greater,  and  hence  climatic  uniformity  was  greater.  The 
greater  uniformity  extended  through  the  year  and  over  all  lati- 
tudes. When,  therefore,  the  mean  surface  temperature  was 
higher,  it  was  also  more  uniform.  Tropical  climates  prevailed  at 
the  poles  as  well  as  at  the  equator.  This  deduction  is  sustained 
by  the  facts  of  palaeontology. 

(2)  Alleged  Antecedent  Habitability  of  Northern  Regions. 
In  the  earth's  cooling  from  a  molten  state  the  diminution  of  sur- 


296  GEOLOGICAL   STUDIES. 

face  heat  would  be  nearly  equal  on  all  sides.  But  the  solar  rays 
would  retard  the  surface  cooling  to  a  greater  extent  in  the  equa- 
torial regions  than  in  the  polar.  Consequently,  the  polar  regions 
would  first  attain  a  habitable  temperature.  Chiefly  on  this 
ground  G.  H.  Scribner  has  argued  that  life  began  at  the  pole. 
On  this  and  other  grounds  President  W.  F.  Warren  has  recently 
maintained  that  the  site  of  Paradise  was  at  the  North  Pole.  Ge- 
ology points  out  the  fact  that  the  north  polar  regions  were  once 
the  site  of  a  luxuriant  fauna  and  flora;  that  many  organic  types 
appear  to  have  emigrated  from  the  north,  and  that  many  remain- 
ing there  are  degenerate  forms;  and  science  and  tradition  afford 
other  support  for  this  startling  doctrine.  We  cannot  yet,  how- 
ever, announce  it  as  a  principle  in  geological  history.  It  may 
safely  be  asserted,  however,  that  the  principle  cited  lends  no  sup- 
port to  the  theory  that  the  first  representatives  of  our  species 
made  their  advent  at  the  pole.  At  the  epoch  of  man's  advent, 
even  if  we  fix  it  in  Tertiary  Time,  the  earth's  geological  progress 
was  so  far  advanced  that  the  polar  climate  had  already  become 
inhospitable;  and  the  location  of  the  Paradise  of  our  first  parents 
at  the  North  Pole  is  an  inadmissible  theory. 

(3)  Ultimate  Total  Dissipation  of  Terrestrial  Heat.     There 
is  no  store  of  heat  in  the  earth  so  great  as  not  to  be  ultimately 
exhausted.     If  the  earth  has  not  already  wasted  its  original  sup- 
ply, the. time  will  necessarily  arrive  when  external  sources  must 
furnish  the  only  supply.     As  a  fact,  the  present  stage  of  terres- 
trial cooling  is  so  far  advanced  that  the  thickened  crust  reduces 
to  an  inconsiderable  pittance  all  the  heat  now  reaching  the  sur- 
face from  the  interior.     Our  climates  already  depend  practically 
on  heat  from  the  sun. 

(4)  Ultimate  Extinction  of  the  Sun.     But  the  sun  itself  is 
cooling,  and  his  destiny  is  just  as  inevitable  as  that  of  the  earth. 
We  cannot,  indeed,  calculate  the  ages  which  must  elapse  before 
the  sun's  light  and  heat  will  cease  to  reach  the  earth.     That  de- 
pends on  the  sun's  present  temperature  and  the  sun's  mass  and 
density.     His  temperature  is  not  accurately  known;  but  from  the 
most  trustworthy  assumptions   it  has  been   calculated   by  New- 


DYNAMICAL   GEOLOGY.  297 

combe  that  the  sun  will  be  as  dense  as  the  earth  in  12,000,000 
years.  These  considerations  point  out  an  inevitable  limit  to  the 
present  order  of  things. 

2.  Extra-Terrestrial  Causes  of  Climates.  Geological 
observation  shows  that  one  or  more  periods  of  extraordinary  cold 
have  passed,  in  the  history  of  the  northern  hemisphere.  Much 
study  has  been  bestowed  on  efforts  to  find  a  cause  for  such  a 
vicissitude.  The  following  suggestions  have  been  made:  (a)  The 
radiating  power  of  the  suri  has-been  less  at  certain  periods;  (b) 
The  earth,  with  the  sun  and  solar  system  have  been  transported 
through  colder  regions  of  space;  (c)  Diminished  absorbent  power 
of  the  atmosphere.  These  causes  would  affect  the  whole  earth 
equally.  The  next  two  (not  indeed  extra-terrestrial)  would  affect 
only  certain  regions:  (d)  A  different  arrangement  of  the  conti- 
nental masses  has  caused  a  different  distribution  of  warm  and 
cold  currents;  (e)  Northern  elevation.  The  following  would 
affect  the  northern  and  southern  hemispheres  alternately:  (/') 
Variations  in  the  amount  of  obliquity  of  the  earth's  axis  to  the 
plane  of  the  ecliptic;  (g)  The  precession  of  the  equinoxes,  or 
direction  of  the  inclination  of  the  earth's  axis  in  reference  to 
perihelion  and  aphelion;  (h)  The  periodic  increase  in  the  eccen- 
tricity of  the  earth's  orbit.  We  cannot  afford  the  space  even  to 
explain  the  three  astronomical  theories  last  mentioned,  and  the 
others  will  be  at  once  intelligible,  or  may  be  thought  o,ut  by  the 
student. 

§  6.     Tidal  Action  in  the  Earth's  History. 

1.  Definitions.  A  tide,  in  general  terms,  is  the  change 
produced  in  the  form  of  a  body  by  the  attraction  exerted  by 
another  body.  Two  spheres  mutually  attracting  become  mutually 
prolate.  The  form  of  each  is  a  prolate  spheroid,  with  its  longer 
axis  in  the  line  passing  through  the  two  centres  of  gravity.  The 
elevations  of  the  prolate  poles  above  the  mean  surface  are  the 
tides.  The  elevation  of  the  pole  opposite  the  tide-producing 
body  is  the  antitide.  The  tide  results  from  the  fact  that  the 
nearer  side  of  the  tide  bearer  is  more  strongly  attracted  than  the 


298 


GEOLOGICAL   STUDIES. 


FIG.  218.— A  DEFORMATIVE  TIDE. 
amis  the  tidal  elevation ;  b  w, 
the  anti-tidal  elevation ;  c  o  and 
d  p  are  the  tidal  depressions. 


centre;  and  the  antitide  from  the  fact  that  the  centre  is  more 
strongly  attracted  than  the  farther  side.  In  the  annexed  dia- 
gram, the  tidal  attraction  is  supposed 
to  come  from  the  side  a.  Then,  a  m 
is  the  tidal,  and  b  n  the  antitidal  ele- 
vation, c  o  and  d  p  are  the  tidal  de- 
pressions. The  tide  raised  in  the 
ocean  by  the  attractions  of  the  moon 
and  sun  are  well  known.  But  it  is 
not  necessary  that  a  liquid  film 
should  exist.  It  is  not  necessary  that 
the  tide-bearing  body  should  be  dis- 
tinctly plastic.  It  has  been  shown 
that  if  the  earth  were  as  rigid  as  glass, 
the  moon's  attraction  would  raise  a 
tide  in  it  three-fifths  as  high  as  the 
tide  in  the  water-covered  earth;  and 
if  the  earth  were  all  steel,  the  tide  would  be  still  one-third  as 
high  as  it  is  at  present.  The  whole  earth  then  yields  to  the  lunar 
tidal  attraction.  There  is  no  matter  so  rigid  as  not  to  be  rela- 
tively plastic  and  yielding  in  the  presence  of  the  enormous  forces 
exerted  upon  each  other  by  the  heavenly  bodies. 

2.  Seismic   Consequences   of  Tidal    Action.    From 
what  has  just  been  stated,  it  appears  that  the  moon's  attraction 
subjects  the  earth's  crust  to  strains  similar  to  those  resulting  from 
secular  contraction.     The  moon  must,  therefore,  contribute  some- 
thing to  earthquake  phenomena.     There  must,  then,  be  a  connec- 
tion in  times  of    occurrence  between  such  phenomena  and  the 
phases  of  the  moon.     Accordingly,  it  has  been  shown,  especially 
by  M.  Alexis  Perrey,  that  these  phenomena  are  of  most  frequent 
occurrence  (a)  When  the  moon  is  in  perigee;  (b)  When  the  sun 
and  moon  are  in  conjunction  or  opposition,  thus   uniting   their 
actions;   (c)  When  the  moon  is  near  the  meridian.     It  cannot  be 
said,  however,  that  tidal  agency  in  earthquakes  is  fully  estab- 
lished. 

3.  Tidal  Evolution  of  Heat.    It  will  at  once  occur  to 


DYNAMICAL   GEOLOGY.  299 

the  student  that  motions  in  the  crust  caused  by  tidal  disturbance 
must  evolve  some  heat,  like  the  motions  resulting  from  contrac- 
tion. But  we  have  not  the  requisite  data  as  yet  for  determining 
whether  or  not  the  heat  generated  in  this  way  is  sufficient  to  ex- 
plain all  the  thermal  phenomena  of  the  earth's  crust,  or  even  any 
important  proportion  of  them.  Here,  however,  are  causes  in 
action,  and  they  must  be  borne  in  mind. 

4.  Tidal  Influence  on  Motions  of  the  Earth  and 
Moon.  (1)  Lagging  of  the  Tide.  If  the  terrestrial  tide  re- 
sponded instantly  to  the  moon's  attraction,  the  summit  of  the  tide 
would  be  always  under  the  moon.  But  owing  to  the  viscosity 
even  of  fluid  substances,  the  tide  lags.  That  is,  the  moon  is 
always  farther  west  than  the  apex  of  the  tide.  In  the  accom- 

I\  iG 


FIG.  219.— ILLUSTRATING  A  LAGGING  TIDE. 

panying  figure,  if  Q  is  the  earth's  centre  and  C  the  position  of 
the  moon,  then  the  apex  of  the  lunar  tide  will  be  at  B  instead  of 
A.  That  is,  the  rotation  of  the  earth  being  in  the  direction  of 
the  arrow,  it  will  have  carried  the  point  A.  to  B  while  the  tide  is 
completing  its  rise  after  the  culmination  of  the  moon. 

(2)  Retardation  of  the  Earths  Rotation.     Now,  when  the 
earth,  the  tide,  and  the  moon  are  in  the  relative  positions  shown 
in  Fig.  219,  the  moon's  attraction  on  the  tidal  protuberance,  in 
excess  of  its  attraction  on  the  more  remote  antitidal  protuberance 
Z>,  tends  to  turn  the  earth  in  a  direction  contrary  to  that  of  its 
actual  rotation.     That  is,  the  earth's  rotation  is  opposed.     The 
length  of    the  day  is  diminished.     Calculation    shows    that  the 
amount  of  this  diminution  is  quite  appreciable. 

(3)  Diminution  of  the  Earths  OUateness.     This  is  a  neces- 


300  GEOLOGICAL    STUDIES. 

sary  accompaniment  of  diminished  velocity  of  rotation.  This 
fact  implies  that  the  equatorial  circumference  of  the  earth  has 
diminished,  during  long  secular  intervals  of  time,  more  than  the 
polar  circumference.  Consequently,  a  greater  lateral  pressure 
has  been  experienced  in  the  latitudinal  (east  and  west)  direction 
than  in  the  longitudinal  direction.  This  excess  of  latitudinal 
pressure  would  produce  effects  having  a  meridional  trend;  and 
this  excess  of  equatorial  shrinkage  would  supplement  the  shrink- 
age due  to  general  contraction.  The  surplusage  in  the  length  of 
the  circumference  thus  resulting,  added  to  the  surplusage  result- 
ing from  general  cooling  contraction,  might  afford  all  the  sur- 
plusage wrought  into  the  folds  and  plications  of  the  earth's 
crust,  and  thus  obviate  a  difficulty  in  the  theory  of  mountain 
making  stated  on  page  292. 

(4)  Increase  of  the  Moon's  Distance.  Referring  again  to 
Fig.  219,  we  may  consider  the  reciprocal  action  of  the  tide  J?  on 
the  moon's  motion  in  the  orbit  HI.  This  influence  is  plainly 
accelerative.  But,  if  the  moon's  velocity  is  increased,  its  cen- 
trifugal tendency  is  increased.  It  therefore  recedes  from  the 
earth  and  revolves  in  a  larger  orbit.  These  actions  and  reac- 
tions have  existed  as  long  as  the  earth  and  moon  have  existed  as 
separate  bodies.  We  must  therefore  contemplate  a  time  when 
the  moon  was  much  nearer  the  earth  than  at  present,  and  conse- 
quently revolved  with  a  higher  velocity. 

5.  High  Primitive  Tides.  On  these  grounds,  it  has 
been  suggested  by  Professor  Ball  that  in  early  times  —  perhaps 
during  the  Palaeozoic  ./Eon  —  the  proximity  of  the  moon  caused 
enormously  high  tides  in  the  oceans,  and  thus  accelerated  the 
processes  of  erosion  and  deposition,  and  shortened  correspond- 
ingly the  time  required  for  the  geological  work  accomplished.  If 
such  increase  of  tidal  action  ever  existed,  the  thickness  and 
coarseness  of  the  strata  would  testify  to  it.  But  the  Palaeozoic 
strata  appear  to  have  been  quietly  deposited,  under  conditions 
not  very  different  from  those  now  existing.  If  we  extend  our 
observations  back  through  the  Eozoic  formations,  we  discover 
some  evidences  of  superior  energy  in  the  geologic  forces,  but  no 


DYNAMICAL   GEOLOGY.  301 

such  indications  of  extreme  violence  as  the  suggestion  of  Pro- 
fessor Ball  implies.  Still,  the  reasoning  is  sound,  and  we  are  yet 
at  liberty  to  conclude  that  extreme  tidal  energy  left  its  record  in 
those  primordial  sediments  which  have  been  in  later  times  com- 
pletely melted  away. 

6.  Ingrained  Meridional  Trends  in  the  Earth's 
Crustal  Structure.  Lunar  tides  existed  on  the  earth  while 
it  was  yet  molten.  They  existed  during  the  incrustive  stage,  and 
were  more  considerable  than  at  present  in  proportion  as  the  cube 
of  the  moon's  distance  was  less.  The  superior  density  and 
viscosity  of  the  molten  fluid  would,  however,  determine  a  lower 
tide  than  if  produced  in  water.  Recurring  again  to  Fig.  219,  it 
is  seen  that  the  moon  tends  to  pull  the  lagging  tide  around 
toward  the  west.  In  a  molten  globe  there  would  be  some  actual 
slipping  westward.  This  would  be  greatest,  on  the  average, 
along  the  equator.  The  effect  of  this  slipping,  on  the  forming 
crust,  would  be  to  impart  a  non-homogeneous  structure.  Lines  of 
structure  running  nearly  north  and  south  would  be  ingrained  in 
the  crust.  So  much  would  result  from  lunar  tidal  action  on  the 
primitive  crust. 

But  the  slow  subsidence  of  the  equatorial  protuberance 
during  the  secular  diminution  of  the  earth's  rotational  velocity, 
would  produce  a  result  of  a  similar  nature.  The  excess  of  lateral 
pressure  in  the  middle  zone  of  the  earth  would  be  analogous  to 
the  action  of  the  moon  on  the  retarded  tide.  Any  results  pro- 
duced would  have  a  meridional  trend.  Meridional  lines  of  struc- 
ture would  determine  meridional  predispositions  to  yield  and 
take  shape,  under  the  action  of  any  causes  affecting  the  perfect 
symmetry  of  the  earth's  surface. 

The  lines  of  meridional  structure  and  predisposition  deter- 
mined by  these  two  causes  were  primordial  features.  Hence,  if 
afterward,  the  secular  cooling  and  contraction  of  the  earth  should 
tend  to  develop  wrinkles  without  determinate  direction,  as 
would  be  the  case,  these  meridional  ingrained  predispositions 
would  give  a  majority  of  them  a  north  and  south  direction.  In 
the  equatorial  zone,  the  excess  of  east  and  west  pressure  would 


302  GEOLOGICAL   STUDIES. 

tend  directly  to  produce  meridional  wrinkles.  Thus  we  discover 
causes  why  the  primitive  mountains  assumed  elongated  forms; 
and  why  the  direction  of  the  elongation  was  approximately  north 
and  south. 

This  theory  is  not  claimed  as  one  generally  recognized  among 
geologists.  The  suggestions  are  recent.  But  some  causes 
operated  to  produce  all  the  results  enumerated  on  page  293  as 
mountain  features  to  be  explained  by  a  final  theory,  and  these 
views  are  submitted  as  at  least  plausible  and  deserving  of  study. 

§  7.     Geotechtonic  and  Scenographic  Results. 

The  dynamic  actions  which  have  given  shape  to  the  earth's 
periphery  are  strictly  subjects  of  geological  investigation.  The 
results  are  inseparably  bound  up  with  the  causes.  The  descrip- 
tion of  mountains,  continents,  oceans,  and  other  physiographic 
features  belongs  to  geology.  Such  descriptions  may  be  gathered 
together  under  a  separate  head  and  designated  "  physical 
geography";  but  so  far  physical  geography  is  only  a  branch  of 
geology.  It  is  a  grouping  of  a  certain  class  of  structural  facts; 
but  without  the  attempt  to  interpret  them  and  ascertain  their 
meaning  and  unity.  Physical  geography  should  be  taught  and 
understood  as  an  essential  part  of  geology. 

It  would  be  deeply  interesting  to  review  here  the  earth's 
physiographic  features,  and  trace  their  connection  with  the 
causes  that  have  been  passed  under  review  in  this  Chapter.  The 
method  of  the  First  Part  of  this  work,  however,  has  led  us  con- 
tinually to  an  observation  of  these  features  as  the  grounds  and 
suggestions  for  the  principles  there  induced.  For  the  present, 
therefore,  we  shall  pass  on  to  other  branches  of  the  science  which 
deserve  prominent  treatment. 


CHAPTER  IV. 
PROGRESS  OF  TERRESTRIAL  LIFE. 

DEFINITIONS.  Each  Age  and  Period  of  the  world's  history 
has  been  characterized  by  its  special  assemblages  of  animals  and 
plants.  Many  of  the  remains  of  these  have  been  imbedded  in  the 
sediments  of  the  time,  and  have  become  fossilized.  When  we 
examine  to-day  the  rocks  resulting  from  these  sediments,  the  fos- 
sil forms  are  disclosed,  and  serve  as  the  stamp  of  the  age  in  which 
they  were  alive.  Fossils  are,  therefore,  a  most  important  means 
for  the  determination  of  a  formation.  We  shall  not,  in  this 
course,  attempt  to  lead  the  student  far  into  this  subject.  We 
have  shown,  in  Studies  XXX-XXXIY,  something  about  the 
method  of  studying  fossils.  In  this  chapter  we  propose  to  give, 
for  convenient  reference,  an  outline  tabular  exhibit  of  the  classi- 
fication of  fossils,  and  sketch  some  of  the  most  prominent  fossil 
types  which  have  appeared  and  disappeared  in  the  history  of 
life. 

Fossilization.  A  fossil  is  whatever  reproduces  for  us  any- 
thing of  the  form  or  structure  of  an  organic  being  no  longer 
living.  It  may  be:  (1)  The  real  substance  of  the  organism,  like 
a  shell,  or  bone,  so  recent  as  to  have  been  little  altered.  (2)  The 
perfect  form  and  structure  of  the  organism,  but  with  the  original 
substance  replaced  by  other  mineral  matter.  This  is  a  true  pet- 
rifaction. The  replacing  mineral  is  commonly  calcite  or  silica; 
sometimes  pyrites,  or  other  substance.  In  fossil  wood  it  is  fre- 
quently opal.  (3)  The  fossil  may  be  a  mere  impression  of  the 
exterior  of  the  organism,  made  originally  in  the  soft  mud  of  the 
sea  bottom.  The  shell,  or  coral,  may  be  completely  removed; 
but,  with  gutta-percha,  putty,  sulphur,  or  plaster,  the  mould  may 
be  filled,  and  the  form  of  the  original  organism  sometimes  very 


304  GEOLOGICAL   STUDIES. 

perfectly  restored.  In  some  cases  the  mould  is  found  filled  with 
stony  matter.  (4)  The  fossil  may  be  a  mere  cast  of  the  interior 
of  a  shell  or  other  organism.  The  soft  muddy  or  sandy  filling  of 
the  interior  became  consolidated,  and  afterward  the  organism 
wasted  away.  Such  casts  often  preserve  very  perfectly  the  mus- 
cular scars  or  vascular  impressions  on  the  interior  of  a  shell. 

Horizontal  Range  of  Fossils.  This  is  simply  the  geographi- 
cal area  over  which  a  fossil  species  may  be  found.  Some  of  the 
older  species  have  been  discovered  in  many  different  regions  and 
countries.  This  wide  range  becomes  of  great  service  in  identify- 
ing formations  at  remote  points.  The  extent  of  the  horizontal 
range  depends  on  the  extent  of  the  uniformity  of  physical  condi- 
tions when  the  animals  lived.  Diverse  conditions  at  distant 
points  necessitated  diverse  faunas.  Thus  it  happens,  sometimes, 
that  equivalent  formations  hold  different  assemblages  of  fossils. 
Vertical  Range  of  Fossils.  This  refers  to  the  occurrence  of 
the  same  species,  or  other  type,  in  formations  older  or  newer, 
throughout  a  certain  vertical  range.  It  implies  that  a  species 
survived  changes  in  physical  conditions  which  separated  succes- 
sive periods,  and  which  exterminated  most  of  its  fellows.  It 
implies  that  the  physical  changes  were  not  great,  or  that  the 
species  possessed  great  tenacity  of  life.  Hence  species  with 
great  vertical  range  are  generally,  also,  species  of  wide  geograph- 
ical distribution.  As  a  rule,  species  are  confined  to  a  single 
formation.  Sometimes  they  range  vertically  into  one  or  more 
higher  formations.  Sometimes,  after  disappearing  from  overly- 
ing strata  of  changed  constitution,  a  species  reappears  in  a  still 
higher  stratum  formed  under  a  recurrence  of  the  former  physical 
conditions.  Its  temporary  disappearance  indicates,  therefore,  not 
extinction^  but  migration  to  some  more  congenial  region. 

Colonies,  so  called  by  Barrande,  are  incidents  of  migrations 
of  faunas.  A  colony  is  an  assemblage  of  fossils  reputed  charac- 
teristic of  a  certain  age,  interstratified  in  a  formation  containing 
its  own  reputed  characteristic  fossils.  Thus  Barrande  brought  to 
light  in  Bohemia  a  colony  of  Silurian  fossils  3,400  feet  deep  in 
the  midst  of  a  Cambrian  group.  In  such  case  it  is  evident  that 


PROGRESS    OF   TERRESTRIAL   LIFE.  305 

the  included  colony  is  not  properly  characteristic  of  a  different 
age.  The  colony,  and  the  fauna  in  which  it  colonized,  were  con- 
temporaneous, but  living  in  different  regions,  separated  by  some 
barrier.  The  removal  of  this  permitted  the  commingling  of  the 
two  populations. 

SECTION    I  — MOST   IMPORTANT   TYPES   OF   PLANTS   AND 
ANIMALS. 

[Numbers  in  parenthesis  refer  to  Figures  in  this  work.] 

I.— PLANTS. 
SERIES  I.— CRYPTOGAMS. 

STEM  I.  THALLOPHYTES. -Consisting  wholly  of  cellular  tis- 
sue.    Growing  mostly  in  fronds,  or  other  spreading  forms, 
without  proper  stems  or  leaves. 
CLASS  I.   ALGAE.  — Those  living  in  the  sea  are  THALASSOPHYTES  (295) ; 

those  in  fresh  water,  HYDROPHYTES. 

ORDER  I.    UNICELLULAR  THALLOPHYTES.— Including  Diatomacece,  of 
microscopic  size,  and  having  silicious  shields.     Other  fossil 
Alg;e  are  not  thoroughly  classified. 
CLASS  II.    FUNGI. -CLASS  III.    LICHENS. -Not   geologically 

important. 

STEM  II,  BRYOPHYTES-(^^^s). 
CLASS  I.   MTJSCINJE. -Moss-like. 

ORDER  I.  HEPATIC/E.— Liverworts.     ORDER  II.  BRYO I DE/E.— Mosses. 
STEM  III.   PTEBIDOPHYTES  (^m^ens). -Vascular  Crypto- 

gams. 

CLASS  I.    FILICACE2E. — Perns.     The  following  Families  are  recog- 
nized : 

Hymenophyllaceas,  Sphenopteridce,  Palteopteridce,  Neuropteridce, 
Cardiopteridce,  Alethopteridce,  Pecopteridae,  Tcenioptvridce. 
Also,  from  stems  we  have  the  genera  Caulopteris,  MegapJiyium, 
Psaronius. 

CLASS  II.    BHIZOCARPE^E.— Hydropterids. 
CLASS  III.    CALAMARIEJE. 

Family  1.   Equisetece.—Rorse-t&ils.      3.    Calamitece.—Cal&mites.      4. 
Annulariece.    Annularia,  Aster ophyllum,  SpTienophyllum. 
CLASS  IV.    LYCOPODIACE^J. 

Family  1.  Lycopodiete.  Psilophyton.  2.  I,epidodendrece.  Lepido- 
dendron,  Ulodendron,  Halonia.  4.  Sigillariece.  Sigil- 
laria,  Stigmaria. 


306  GEOLOGICAL   STUDIES. 

SERIES  II.— PHANEROGAMS. 

STEM  IV.    G-YMNOSPERMS.-Seed  not  inclosed. 

ORDER  I.    C YCAD AC E/E.—  Carboniferous  Whittleseya  arid  many  Meso- 

zoic  genera. 

ORDER  II.    CORDAITE/E.— Cordaites. 
ORDER  III.    CONIFERS.— Pines,  Firs,  etc. 
STEM  V.   ANG-IOSPERMS.-Seed  inclosed. 
CLASS    I.     MONOCOTYLEDONS.— Endogeiis.      Mostly    parallel- 
veined  leaves. 
CLASS  II.     DICOTYLEDONS.— Exogens.     Netted-veined  leaves. 

II.  —  ANIMALS. 

STEM  I.-PROTOZOA. 

Chiefly  microscopic,  with  no  definite  typical  form,  without  specialized  organs, 

and  mostly  with  asexual,  as  well  as  sexual  reproduction. 

CLASS  I.      MONERA. — Of    completely    homogeneous,    structureless 

protoplasm. 

CLASS  II.    RHIZOFODA.  —Body  consisting  chiefly  of  simple  sarcode. 
ORDER  I.    FORAMINIFERA  (Polythalamia). —Having  a  one-chambered 
or  many-chambered  shell,  calcareous,  rarely  sandy,  silicious, 
or  chitinous. 

SUB-ORDER  L    IMPERFORATA.—  Receptaculites.     II.  PER- 
FORATA. —  Globigerinaj  Nummulites,  Orbitoides,  Fusu- 
lina,  Eozoon.     (220,  222.) 
ORDER  II.   RADIOLARIA  (Polycistina).     III.  L03OSA.     Amceba.     (221.) 

STEM  II  -CCELENTERATA. 

CLASS   I.    SPONGLZE. — (Porifera.     Amorphozoa.)     Sponges. 
CLASS  II.    ANTHOZOA.      (Polypi.     Zoophyta.)     Radiated,  mostly 
with  a  calcareous  skeleton,  having  radial  septa.     Skeleton 
known  as  coral. 

ORDER  I.   ALCYONARIA.— (Octocoralla.)     With  eight  radial  divisions. 
ORDER  II.    ZOANTHARIA. —  Having  twelve    or    more  radial  divisions. 

Most  Paleozoic  corals  belong  here. 

SUB-ORDER  ANT1PITHAR1A.— Having  an  internal  horny  axis. 
SUB-ORDER  A  C  TIN  ARIA.—  Without  calcareous  skeleton.     Not 

fossilized. 
SUB-ORDER  3IADREPORAR1A  (Zoantharia   Sclerodermata).— 

Having  a  calcareous  skeleton. 

Group  1.     Tetracoralla  (Rugosa). — Cup  Corals.     Four  systems 
or  fascicles  of  septa.     See  Studies  XXX,  XXXI. 


PROGRESS    OF   TERRESTRIAL   LIFE.  307 

Family  l.  inexpleta.— Tnterseptal  chambers  empty  or  with  feeble 
dissepiments  —  tabular  and  cellular  contents  wanting. 
Septa  well  developed.  Cyathiform,  simple.  Amplexus 
(114,  115,  118,  119). 

Family  2.    Expleta. — Tabulae  or  cells  or  both  fill  the  visceral  cavity. 

SUB -FAMILY  DIAPHRAGMATOPHORA. —  Tabulae  complete;  cellular  en- 
dotheca  wanting  or  feebly  developed.  Septa  regularly 
radiate.  Zaphrentis  (112,  113,  117),  Streptelasma  (122- 
124). 

SUB-FAM.  PLEONOPHORA. — Tabulae  incomplete,  present  only  in  central 
part  of  visceral  cavity;  cellular  tissue  in  peripheral  part. 
Oyathophyllum  (116,  120,  121),  Heliophyllum  (130,  132» 
133),  Acervularia  (138,  139),  Diphyphyllum  (141-143), 
Lithostrotion  (140;. 

SUB-FAM.  CYSTOPHORA.—  Whole  interior  filled  with  vesicular  tissue. 

Cystipliyllum  (134-136). 

Group  2.     Hexacoralla. — Septa  mostly  in    multiples    of    six. 
Here  belong  the  "honey-comb"  corals. 

Family  1.  foritidce. —  Compound,  cells  united,  small.  Septa  few, 
mostly  rudimentary.  Walls  perforated. 

SUB-FAM.  FAVOSITIX^E. —  Massive,  without  ccenenchyma.  Cells  long, 
prismatic,  divided  by  numerous  tabulae.  Walls  pierced  by 
numerous  perforations.  Septa  six  or  twelve,  often  reduced 
to  mere  longitudinal  raised  striae  on  the  walls.  Favosites 
(144-149,  152),  Alveolites  (153,  154),  Limaria  (155,  156), 
Cladopora  (157,  158). 

CLASS  III.    HYDBOMEDUS^E  (Hydrozoa).—  Hydras  and  Sea  Net- 
tles.    Fixed,  polyp-like,  small,  undivided  by  radial  septa. 
Skeleton  calcareous,  chitinous,  or  wanting. 
ORDER  HYDROIDA  (Hydrophora). 

Family  Stromatoporidce.—  [Probably  a  "comprehensive"  type  unit- 
ing characters  of  Foraminifera,  Sponges,  Hydroida,  and 
Tetracoralla.  Probably  also  Eozoon  belongs  in  near  rela- 
tion] (223-227). 

SUB-ORDER  GRAPTOLITID^E. 

STEM  III.-ECHINODERMATA. 

CLASS  I.  CRINOIDEA.— Sea  Lilies.  Crinoids.  Supported  by  a 
stem.  Visceral  organs  inclosed  by  calcareous  plates  sym- 
metrical in  form  and  disposition.  Five  to  ten  arms  spring 
from  the  border  of  the  cup,  and  these  are  fringed  with 
pinnules. 


308  GEOLOGICAL   STUDIES. 

ORDER  I.    ENCRINOIDEA  (Palaeocrinoidea)  (233).  — Armed  Sea  Lilies. 

Rliizocrinus  (232),  Forbes  iocrimts  (234). 
ORDER  II.    CYST01DEA.— Cystids.     Short-stemmed  or  sessile.     Arms 

feebly  developed.     Palaeozoic.     Caryocrinus. 

ORDER  III.  BLASTOIDEA.— Nut  shaped  or  oval,  armless,  short- 
stemmed.  Cup  of  thirteen  regularly  disposed  principal 
pieces.  Pentremites. 

CLASS  II.    ASTEROIDEA.—  Sea  Stars.     Star  Fishes. 
CLASS  III.    ECHINOIDE A.  — Sea  Urchins. 
CLASS  IV.    HOLOTHTJROIDE A.— Sea  Cucumbers.    Holothurians. 

STEM  IV.-VERMES. 

The  four  lower  classes  of  Worms  are  scarcely  known  fossil. 
CLASS  ANNELIDA.— With  cylindrical  segmented  body  and  chitin- 
ous  integument.   Serpula,  Spirorbis?  Cornulites,  Scolitlius. 

STEM  V.- MOLLUSC  A. 
DIVISION  A.-  MOLLUSCOIDEA. 

CLASS  I.    BBYOZOA  (Polyzoa).—  Colonies    of     small    animals    sur- 
rounded by  a   membranous   or  calcified  integument,  and 
forming  branched   moss -like   or  membranous  compound 
structures.     In  general  aspect  much  resembling  Hydrozoa. 
Sub-Class  I.    Entoprocta. —  No  representatives  fossil. 
Sub-Class  II.    Ectoprocta. 

Family  4.    Fenestellidce. —  Fenestella,  Polypora,  Archimedes. 
Family  5.    Ptilodictyonidce. — Pilodictya,  Coscinium. 
Family  1O.    Chcetetidce. —  In  masses  resembling  diminutive  Favosi- 

tidcB,  but  without  connecting  pores.     Monticulipora. 
CLASS  II.    BBACHIOPODA   (Palliobranchiata).—  Brachiopods. 

Compare  Studies  XXXIII  and  XXXIV. 
ORDER  I.   PLEUROPYGIA.— Hinge     structure     and     arm     supports 

wanting. 

Family  1.    Lingulidce. — Lingula,  Lingulella,  Lingulepis,  Glottidia. 
Family  2.    Obolidce. — Obolus,  Oboiella,  Trematis. 
Family  3.    Discinidce. — Discina,  Orbiculoidea. 
Family  4.    Trimerellidce. —  Monomeretta,  Trimerella,  Dinobolus. 
Family  5.     Craniadce. —  Crania. 
ORDER  II.  APYGIA — Always  calcareous,  with  hinge  structure.     With 

or  without  arm-supports. 

Family  1.    Productidce. — Producta,  Clionetes,  Productella. 
Family  2.    Strophomenidce. — Ortllis  (166,  171),  Streptorhynchus,  Or- 
thisina,  Strophomena  (167,  168,  190,  192),  Leptcena,  Trop- 
idoleptus,  Skenidium,   Vitulina. 


PROGRESS    OF   TERRESTRIAL    LIFE.  309 

Family  3.    Koninckinidce. — Koninckia.     None  American. 
Family  4.    Spiri  fer  idee.— Spin f era  (161,  162,  164,  165,  172,  174), 

Spiriferina,     Cyrtia,    Cyrtina  (170).     Syringothyris  (181, 

183),    Sprigera  (179,  180),    Nucleospira,    Merista,    Meri- 

stella,  Retzia,  Uncites. 
Family  5.    Atrypidce. — Atrypa    (175-177),     Cwlospira,     Zygospira 

(178) 
Family  6.    Rhynchonellidce. — Rhynchonella,      Leiorhynchus,      Di- 

merella,  Camerella,  Penlamerus,  Stricklandia. 

Family  7.    Str ing ocephal idee. — String  ocephalus.      None  American. 
Family  8.    Thecideidce . — Thecia.     None  American. 
Family  9.    Terebratulidce. —  Terebratula     (184-186),       Cryptonella, 

Rensselceria,  Meganteris,  Centronella  (187,  188). 

DIVISION  B.- MOLLUSC  A  Proper. 

CLASS  I.    LAMELLIBRANCHIATA   (159,  160).— Equivalve   Bi- 
valves.    See  Study  XXXIII. 

ORDER  I.  ASIPHON! DA. —  Mantle  lobes  divided,  siphon  wanting,  pal- 
lial  impression  without  sinus. 

DIVISION  A.  MONOMYARIA.— Onlj  one  (hinder)  adductor 
muscle.  Ostrea,  Gfryphcea,  Exogyra,  Pernopecten,  Avicu- 
lopecten. 

DIVISION  B.  ffETEROMYARIA.—Two  unequal  adductors. 
Cartilage  separated  in  numerous  isolated  pits  or  furrows. 
Avicula.  Pterinea. 

DIVISION  C.    HOMOMYARIA.—Two  equal  adductors.     Cyrto- 

donta,  Nucula,  Palceoneilo,  Schizodus,  Cardinia. 

ORDER  II.  SIPHON  I  DA. —  Siphon  present;  mantle  lobes  more  or  less 
united. 

DIVISION  A.  INTEGRIPALLIATA.—Pa\\i&\  impression  with- 
out sinus.  Lucina,  Conocardium,  Cypricardinia,  San- 
guinolaria. 

DIVISIONS.    SINUPALLIATA. 

Solenopsis,    Cardiomorpha,    Edmondia,   Allorisma,   San- 
guinolites. 

CLASS  II.     GASTEROPODA    (Glossophora.      Cephalophora).— Uni- 
valves. 

Sub-Class  I.  Scaphopoda. — Tubular,  open  at  both  ends.  Den- 
talium. 

Sub-Class  IH.    Gasteropoda  Proper. 

ORDER  I.  PROSOBRANCHIA.— Gills  anterior  to  the  heart.  Metop- 
toma,  JBellerophon,  Cyclonema,  Holopea,  Platyceras,  Pla- 
tyostoma,  Loxonema. 


310  GEOLOGICAL   STUDIES. 

ORDER  II.   HETEROPODA.— Mostly  naked.     Unimportant    palseonto- 

logically. 

ORDER  III.  OPISTHOBRANCHIA.— Scarcely  known  as  Paleozoic. 
ORDER  IV.  PULMON  AT  A.— Air-breathing.     Pupa,  Dendropupa. 
Sub-Class  IV.    Pteropoda.— Tentaculites,  Hyolithes,  Conularia. 

CLASS  III.    CEPHALOPODA  (Cephalophora)  Cephalopods. 

ORDER  TETRABRANCHIATA   (236).— Having    an    external    chambered 

shell. 
SUB-ORDER  1.    NAUTILOIDEA.—  Shell      straight,     bent,     or 

coiled.    Sutures  mostly  simple  or  slightly  sinuate.    Siphonal 

cornets  directed  backwards. 
Family  1.    Orthoceratidce. —  Straight  or  slightly  bent.     Orthoceras. 

(235,  237.) 
Family  3.    Cyrtoceratidce. —  Simply  bent.     Cyrtoceras  (238),  Phrag- 

moceras. 
Family  4.    Nautilidce. —  Coiled  in  a  plane.     Gyroceras  (239),  Litu- 

ites,     Nautilus. 

Family  5.    Trochoceratidce. —  Coiled  in  a  conical  spire.    Trochoceras. 
SUB-ORDER  II.    AMMONOIDEA  (240).— Shell  coiled  variously 

or   straight.     Suture   line   undulate,  lobed   or  foliaceous. 

Siphon  cylindrical,  marginal. 
Family  1.    Clymenidce. —  Umbilicus  wide.      Siphon   internal.      Cly- 

menia. 

Family  2.    Goniatitidce. —  Siphon  thick,  external.     Goniatites. 
A  large  Sub-Order,  but  the  remaining  genera  are  post-Palfeozoic. 

STEM  VI.- ARTHROPOD  A. 

CLASS  I.  CRUSTACEA.—  Respiration  aquatic.     Exoskeleton  chitin- 

ous  or  sub-calcareous. 

Sub-Class  II.    Cirripedia. — Attached  when  adult. 
Sub-Class  III.     Entomostraca. —  Carapace  horny,    composed  of 

one  or  more  pieces. 
ORDER  I.    OSTR  AGO  DA.— Carapace     of     two     valves.      Leperditia, 

CytJiere. 

ORDER  IX.  PHYLLOC A Rl DA —Feet  serving  as  gills.  Ceratiocaris. 
ORDER  X.  TRILOBITA  (231).— Body  more  or  less  trilobed.  Cephalic 
shield  usually  with  a  pair  of  sessile  eyes.  Thorax  with 
movable  segments,  and  caudal  shield  (pygidium)  with  con- 
solidated segments.  Paradoxides  (228),  Dikellocephalus, 
Phacops,  Calymene  (229,  230),  Proetus,  Lichas,  Acid- 
aspis,  Asaphus,  Illcenus. 


PKOGRESS    OF    TERRESTRIAL    LIFE.  311 

ORDER  XI.     MEROSTOMATA. 

Eurypterus,  Pterygotus. 
Sub-Class  IV.    Malacostraca. 
CLASS  II.    ARACHNID  A. —  Scorpions  and  Spiders. 

ORDER  I      PEDIPALPI. —  Scorpions.     Abdomen  distinctly  segmented. 
ORDER  II.    ARANEIDA.— Spiders.     Head  and  thorax  consolidated. 
CLASS  III.    MYRIAPODA. —  Myriapods.     Xylobius,  Archiulus. 
CLASS  IV.    INSECTA. 

STEM  VII.-VERTEBRATA. 

CLASS  I.    PISCES.— Fishes. 

ORDER  I.    TELEOSTEI. —  Common  bony  fishes.     Not  Palasozoic. 
ORDER  II.    GANOIDEI. —  Endoskeleton  generally  only  partially  ossified. 
Exoskeleton  in  the  form  of  ganoid  scales,  plates,  or  spines. 
Caudal  fin  mostly  unsymmetrical  or  "  heterocercal ",  but 
sometimes  "homocercal." 

DIVISION  I.  LEPIDOGANOIDEI.—~&xoskeletou  of  scales  of 
moderate  size.  Endoskeleton  partly  ossified.  Palceonis- 
cii8,  Onychodus  (342),  Lepidosteus  (249-251). 

DIVISION  II.  PLACOGANOIDEL—  Head  and  more  or  less  of 
the  body  protected  by  large  ganoid  plates.  Cephalaspis 
(245),  PtericUhys  (244),  Coccosteus  (246),  Bothriolepis  (247), 
Scaphaspis,  Palc&aspis,  Diniclithys  (241). 

ORDER  III.  ELASMOBRANCHII    (Selachia,    Placoidei).— Sharks,    Rays, 
and  ChimEerae.     Skull  and  lower  jaw  well  developed,  but 
no  cranial  bones.     Vertebral  column  cartilaginous.     Exo- 
skeleton placoid,  consisting  of  grains  or  tubercles. 
SUB-ORDER  I.  HOLOCEPHALL— Jaws  covered  by  broad  plates. 
SUB-ORDER  II.   PLAG10STOML—  Sharks  and  Rays. 

SECTION  I.    CESTRAPHORI  (243). —  Back  teeth  obtuse.     Acrodus, 

Onchus. 

SECTION  II.    SELACHII  —  True  Sharks  and  Dog  Fishes. 
SECTION  III.    BATIDES. —  Rays  and   Skates.     Body  transversely 

flattened. 

ORDER  IV.    DIPNOI  (Protopteri).— Notochord  persistent.     Ceratodus. 
CLASS  II.    AMPHIBIA.— Frogs,    Toads,    Salamanders,    Crecilians, 

and  extinct  Labyrinthodonts. 
ORDER  I.    URODELA  (Ichthyomorpha). —  Tailed  Amphibians.    Notear- 

lier  than  Permian. 

ORDER  II.  ANOURA  (Batrachia.  Theriomorpha).— Frogs  and  Toads 
or  Tailless  Amphibians.  Not  known  earlier  than  Ter- 
tiary. 


312  GEOLOGICAL   STUDIES. 

ORDER  IV.  LABYRINTHODONTA.— All  extinct.  Salamandriform.  Pro- 
tected with  sculptured  bony  plates.  Teeth  with  "laby- 
rinthine ''  structure. 

SECTION  I.  EUGLYPTA. —  Cranial  bones  strongly  sculptured.  Lab- 
yrinthodon. 

SECTION  VI.  GANOCEPHALA  (Archegosauria). — Vertebral  column 
notochordal.  Archegosaurus,  Trimerorachis,  JRachitomus, 
Eryops,  Amphibamus. 

SECTION  X.  MICROSAURIA. —  Ossification  of  limbs  incomplete. 
Dendrerpeton,  Hylonomus,  Hylerpeton,  Sauropus. 

Other  American  Labyrinthodonts:  Tuditanus,  Leptophractus, 
Pelion,  Baphetes,  Colletosaurus,  Dictyocephalus,  Cricotus. 

CLASS  III.    REPTILIA. 

ORDER  I.  CM  ELON I  A.— Turtles  and  Tortoises.     All  post-Pala3ozoic. 
ORDER  II.   PLESIOSAURIA    (Sauropterygia).— Head    small    and    neck 

long.     Plesiosaurus  (254),  Nothosaurus,  Simosaurus,  Plio- 

saurus,  Elasmosaurus  (255),  Cimoliosaurus. 
ORDER  III.  LACERTILIA.— Lizards.     Telerpeton,  Centemodon. 
ORDER  IV.  PYTHONOMORPHA  (Mososauria).—  Body     very    elongate. 

Mososaurus,  Leiodon,  Tylosaurus,  Lestosaurus  (256),  Cli- 

dastes,  all  Cretaceous. 

ORDER  V.  0 PH I Dl A.— Serpents.     Palceophis,  Boavus,  Limnophis. 
ORDER  VI     ICHTHYOSAURIA  (Ichthyopterygia).— Marine.    Ichthyosau- 
rus (252). 
ORDER  VII.  BAPTANODONTA.—  Like  Ichthyosaurus,  but  without  teeth. 

Baptanodon  (253). 

ORDER  VIII.  CROCO  DILI  A.— Crocodiles,  Alligators,  and  Ga  vials. 
ORDER  IX.   DICYNODONTIA.— Jaws  beak-like,  resembling  Turtles.    Ou- 

denodon  (263),  Dicynodon  (264). 
ORDER  X.  THERIODONTA. —  Dentition  of  carnivorous  type.  Cynodraco 

(262),  Lycosaurus  (261). 
ORDER   XI.    PTEROSAUR! A.— Flying    Saurians.      Pterodactylus  (265), 

Pteranodon,  Dimorphodon  (266). 
Sub-Class  Dinosauria  (according  to  Marsh). 
ORDER  I.     SAUROPODA. —  Herbivores.      Premaxillaries     with    teeth. 

Plantigrade. 

Families:    Atlantosauridce,  Diplodocidce,  Morosauridce . 
ORDER  II.  STEGOSAURI A.— Plated  Lizards.    Herbivorous.    Post-pubic 

present. 

Families:    Stegosauridce,  Scelidosauridce. 
ORDER  III.  ORNITHOPODA.— Feet  bird-like.     Herbivorous. 

Families:     Camptonotidce,  Iguanodontidce  (258-260),  Hadrosau- 

rid<e  (258). 


PROGRESS    OF   TERRESTRIAL    LIFE.  313 

ORDER  IV.  THERO  POD  A. —  Beast-footed.     Carnivorous. 

Families:  Megalosauridce,  Labrosauridce,  Zanclodontidce ,  Am- 
phisauridce. 

Also  SUB-ORDERS  :    CCELURIA,  COMPSOGNATHA,  CERATOSAURIA. 
CLASS  IV.    AVES.— Birds. 

Sub-Class  I.    Odontornithes. — Birds  with  teeth   [according  to 

Marsh]. 

ORDER  I.    ODONTOLC>£.— Teeth  in  grooves.     Hesperornis  (269-271). 
ORDER  II.    0 DO NTOTORM/E.— Teeth  in  sockets.     Ichthyornis  (268), 

Apatornis. 
ORDER   III.    SAURURxE.— Teeth.     Tail  longer  than  body.     Archceop- 

teryx  (267). 

Sub- Class  II.    Ratitee. —  Sternum  without  a  prominent  keel. 
Sub-Class  III.    CarinataB. —  Sternum    with    a    prominent    keel. 

Ordinary  birds. 
CLASS  V.    MAMMALIA. 

Sub-Class  I.    Ornithodelphia  (Monotremata). —  Oviparous. 
Sub-Class  II.    Didelphia  (Marsupialia). — Pouched  Mammals  (272- 

277). 

DIVISIONS:  DIPROTODONTIA,  POLYPROTODONTIA. 
Sub-Class  III.    Monodelphia  (Eutheria). —  Placental  Mammals. 
ORDER  I.    EDENTATA.     SUB-ORDERS:  PHYTOPHAGA,  ENTOMOPHAGA. 
ORDER  II.    SIRENIA.—  Manatee  and  Dugong. 
ORDER  III.    CETACEA.— Whales,  Dolphins,  and  Porpoises. 

Families:    Balcenidce,   Catodontidce,  Delphinidce ,  IHiynclioceti, 

Zeuglodontidte. 

SUPER-ORDER  UNGULATA.— Hoofed  Mammals  [according  to  Marsh], 
ORDER  I.     HYRACOIDEA.— No  canines.     Hyracotherium,  Hyracodon. 
ORDER  II.     PROBOSCIDEA.— Elephantine  Mammals.      Elephas,  Mas- 
todon, Dinotherium  (289). 

ORDER  III.  AMBLYDACTYLA  (Amblypoda,  Cope).— A  theoretical  type 
from  which  diverged  two  sub-orders,  DINOCERATA  and  Co- 
RYPHODONTIA,  the  former  with  Uintatherium  (284,  285), 
Dionceras  (286),  Tinoceras  (287) ;  the  latter  with  Corypho- 
don  (Bathmodon)  (278-280). 
ORDER  IV.  CLINODACTYLA. 

SUB-ORDER  I.    MESAXONIA  (Perissodactyla).— Generally  odd- 
toed. 

Families:    Mhinoceridce ,  Tapiridce,  Lymnohyidce,  Erontother- 
idce  (288),  Falceotherldce,    Maehrauchenidce,  Equidce  (290). 
SUB-ORDER  II.     PARAXONIA    (Artiodactyla).—  Mostly    even- 
toed. 

DIVISION  I.  OMNIVORA,  with  Families:  Hippopotamidce,  Su- 
idce,  Hyopotamidce,  Xiphodontidce,  Anoplotheridce, 
Oreodontidce. 


314  GEOLOGICAL   STUDIES. 

DIVISION  II.  RUNINANTIA,  with  Families:  Camelida?,  Tragu- 
lidw,  Cervidce,  Camelopardidce,  Antilopidce,  Ovidce, 
Bovidce. 

ORDER  TILLODONTIA.— Molarsas  in  Ungulates.  Canines.  Plantigrade 
and  pentadactyl.  Unguiculate?  Families:  Tillother- 
ida>  (281),  Stylinodontidce . 

ORDER  TOXODONTI A,— Allied  to  Ungulates,  Rodents,  and  Edentates. 
ORDER  CARNIVORA. 

SECTION  I.    PINNIPEDIA. —  Seals  and  Walruses. 

SECTION  II.  PLANTIGRADA. —  Bears.  Walking  on  whole  length 
of  foot. 

SECTION  III.  DIGITIGRADA. — Walking    on    the    toes.     Families: 

Mustilidce,  Viverridce,  Hycenidce,  Canidte,  Hyivnodonti- 
dte,  Felidce. 

ORDER  RODENTIA.— Gnawing  Mammals.  Families:  Leporida>,  La- 
gnmyidce,  Cavidce,  Hystricidce,Cercolabid<je,Octodontida5, 
Chinchillidfe,  Castorida;,  Muridce,  Dipodidw,  Myox- 
idce,  Sciuridce. 

ORDER  CHEIROPTERA —Bats.     Nydilestes,  Nyctitherium. 

ORDER    INSECTIVORA, — Families:    Talpidce,  Soricidce,  Erinaceidtv. 

ORDER  QUADRUMANA,—  DIVISION  I.    STREPSIRHINA  (Prosi- 

mise). —  Lemurs.      Families:      Lemuridce,     Lemur avidce , 
Limnotheridce . 

DIVISION  II.    PL  A  TYRHINA.—  Tailed  Monkeys. 
Dl  VISION  III.    CA  TARHINA.— Including  Anthropoid  Mon- 
keys. 

§  2.     Nature  of  the  Succession  of  Organic  Forms. 

The  foregoing  tables  are  a  systematic  exhibit  of  the  larger 
types  of  plants  and  animals  which  appeared  on  the  earth  in  the 
progress  of  geological  time,  and  which  continue,  for  the  greater 
part,  to  dwell  in  the  waters  and  upon  the  land,  of  the  modern 
world.  No  Class  of  animals  once  existing  has  totally  disappeared. 
Only  a  very  few  Orders  have  become  extinct  —  and  these  chiefly 
Vertebrates,  dwellers  on  the  land,  where  the  vicissitudes  of  cli- 
mate and  other  conditions  have  been  most  directly  and  most 
severely  felt.  Scarcely  a  marine  Order  is  found  extinct.  A 
large  majority  of  the  marine  Families  still  survive. 

Some  further  inferences  of  a  fundamental  character  derived 
from  palseontological  studies  should  be  here  enunciated. 


PROGRESS   OF  TERRESTRIAL   LIFE.  315 

1.  The  Succession  of  Organic  Forms  has  been  a  general 
Progress  from  lower  to  higher.  The  lowest  position  in  which 
organic  remains  have  been  found  is  in  the  Laurentian.  We  find 
here  mere  traces  of  organisms  related  apparently  to  some  of  the 
lowest  and  simplest  creatures  now  living.  We  shall  presently 
give  them  a  more  particular  description. 

Searching  through  the  overlying  Huronian  strata,  we  find  no 
certain  evidences  of  the  former  existence  of  life.  But  immedi- 
ately on  entering  the  Cambrian  strata,  such  evidences  are  very 
abundant,  and  they  never  fail  through  all  the  higher  formations. 

Throughout  the  Cambrian,  the  fossil  remains  pertain  exclu- 
sively to  Invertebrates.  During  the  Cambrian  were  introduced 
all  the  leading  Clases  of  Molluscs  now  known.  Also  some  char- 
acteristic Class  types  of  Coalenterata,  Echinodermata  and  Arthro- 
poda.  There  are  also  indications  of  Vermes.  So  all  the  Stems 
or  Subkingdoms  of  animals  now  known,  except  Vertebrates, 
have  been  upon  the  earth  from  Cambrian  times.  But  the  Classes 
were  low;  the  Orders  represented  were  low  in  their  respective 
Classes;  and  the  Families  were  low  in  the  Orders  to  which  they 
belonged.  This  is  a  general  law. 

Before  the  close  of  the  Silurian,  Fishes  existed.  These  are 
the  lowest  Class  of  Vertebrates;  and  the  Orders  represented  were 
low  in  their  Class.  They  were  not  well  defined  and  character- 
istic Fishes.  The  true  Fishes  appeared  in  the  Mesozoic  Ages. 
But  the  Palaeozoic  fishes,  if  we  call  them  such,  became  very  abun- 
dant and  powerful,  and  constituted  what  we  may  style  a  ruling 
dynasty  until  the  approach  of  the  Carboniferous  ^Eon.  The  Silu- 
rian and  Devonian  fauna  was  thus  a  great  advance  on  that  of 
the  Cambrian. 

The  time  which  had  now  elapsed  was  enormous  beyond  com- 
putation; but  only  marine  animals  had  been  in  existence.  Next, 
in  approaching  and  entering  the  strata  of  Carboniferous  time,  we 
discover  remains  of  Amphibia.  Fishes  still  existed;  but  Am- 
phibia were  the  highest  type;  and  they  attained  such  dimensions, 
were  clad  in  such  armor,  and  ramified  in  genera  and  species  so 
numerous,  that  they  became  strictly  the  dominant  type  in  the 


316  GEOLOGICAL   STUDIES. 

animal  world.  This  was  the  easier  because  the  hugest  of  the 
armored  fishes  had  mostly  disappeared.  These  air  breathers  in 
adult  life  were  a  further  advance  in  the  grade  of  organization 
on  the  earth. 

Next  came  the  Class  type  of  Reptiles.  They  expanded  enor- 
mously during  the  Mesozoic  ./Eon.  The  Fishes  and  Amphibians 
became  subordinate.  This  was  a  reign  of  Reptiles.  Toward  the 
close  of  the  Mesozoic,  Birds  began  to  appear  —  first,  with  long 
reptilian  tails  and  toothed  jaws;  then  with  toothed  jaws  and 
shortened  tails;  then  under  the  typical  forms  of  Birds  —  Ratitce,, 
Cursores,  or  Running  Birds  first,  and  CarinatCB,  or  Perching  and 
Flying  Birds  next.  So  here  was  further  exemplified  the  principle 
of  progress  which  had  been  operative  from  the  beginning. 

Next,  coming  to  the  study  of  Tertiary  strata,  we  discover  the 
remains  of  many  Mammals.  They  had  begun  already  to  exist  in 
a  feeble  way,  as  far  back  as  the  Jurassic  Age  —  probably  earlier. 
But  here  they  became  dominant.  They  were  not  only  the  highest 
in  rank;  they  attained,  in  many  cases,  gigantic  dimensions,  and 
were  provided  with  formidable  means  of  offence.  They  were  the 
faunal  characteristic  of  the  Tertiary. 

Lastly,  after  all  the  foregoing  histories  had  been  enacted, 
man  camera  ikiiWscene.  He  is  the  last  term  of  a  long  progress. 

2.  The  earlier  representatives  of  Class  and  Ordinal  Types 
were  generally  Comprehensive.  The  individual  animal  was  a 
characteristic  example  of  its  Order  or  Family,  but  united  in  itself 
some  characters  of  other  orders  and  families  —  sometimes  of  sev- 
eral orders  or  families.  The  associated  characters  were  to  be  sep- 
arated in  later  time,  and  organized  in  an  ordinal  or  family  type, 
or  even  a  class  type,  more  clearly  defined.  Thus  the  early  fishes 
retained  'some  of  the  plated  characteristics  of  Crustaceans,  and 
perhaps  more  important  affinities  with  certain  Tunicates,  and  also 
some  characteristics  which  later  were  to  belong  to  Amphibians 
and  Reptiles.  Amphibians  breathed  like  Fishes  when  young,  and 
like  Reptiles  when  adult.  They  were,  and  still  remain,  a  "  com- 
prehensive type."  The  Reptiles,  when  they  arrived,  combined, 
with  proper  reptilian  characters,  some  others  which  were  ichthyic 


PROGRESS    OF   TERRESTRIAL    LIFE.  317 

—  as  if  inherited  from  the  fishes.  The  earliest  birds,  in  their 
teeth  and  long  vertebrated  tails,  still  clung  to  characteristics  of 
a  dynasty  passed  away,  and  were  also  a  comprehensive  type.  The 
same  principle  is  strikingly  exemplified  in  the  whole  Tertiary 
history  of  the  Mammals.  It  was  a  law  in  the  succession  of  life. 

Thus,  we  must  not  conceive  successive  types  of  organization 
as  separated  from  each  other  by  sharp  and  fixed  lines.  They  rise 
into  prominence  like  waves  of  the  sea,  blending  on  their  borders 
with  contiguous  developments  of  organization,  and  then  gradu- 
ally sinking  again,  to  give  place  to  another  swell  in  the  ocean  of 
life. 

3.  The  graduation  in  the  organic  succession  is  not  complete, 
so  far  as  known.  Here  we  must  first  announce  the  fact,  and 
then  append  a  reflection.  The  "  missing  links  "  or  "  gaps  "  in 
the  organic  succession  are  facts  of  importance.  Let  us  enumer- 
ate some  of  them:  (1)  Between  Eozodn,  the  first  known  animal, 
and  the  Cambrian  forms,  next  known.  (2)  Between  Cambrian 
Invertebrates  and  Silurian  Fishes.  (3)  Between  Fishes  and  Am- 
phibians. (4)  Between  Mammals  and  older  Vertebrates.  (5) 
Between  Man  and  lower  Mammalia.  To  these  some  persons  add 
(6)  Between  Inorganic  Matter  and  Eozodn.  (7)  Between  Un- 
intelligent organization  and  Intelligence. 

Our  first  knowledge  of  a  type  presents  it  under  a  somewhat 
complete  development.  Our  contemplation  of  the  succession  of 
dominant  types  reveals  a  series  of  high  wave  crests,  which  give 
the  impression  of  sharply  distinct  advents  of  organic  types  into 
existence.  Hence  the  revelation  of  "  gaps "  is,  at  first  view,  a 
glaring  fact. 

But  when  we  consider  the  facts  of  palseontological  history  a 
little  more  closely,  we  discover:  (1)  Even  if  the  actual  graduation 
were  originally  complete,  we  could  expect  to  acquire  only  a  broken 
knowledge  of  it,  because  (a)  only  a  small  fraction  of  the  earth's 
surface  has  been  explored  for  fossils,  or  ever  can  be;  (b)  in  no 
locality  have  the  rocks  been  completely  investigated;  (c)  if  all 
the  rocks  everywhere  were  completely  investigated,  we  could  not 
expect  to  discover  a  complete  record  of  past  life,  since  the  greater 


318  GEOLOGICAL   STUDIES. 

part  of  the  forms  once  living  have  totally  perished.  Hence,  miss- 
ing links,  even  if  irrecoverable,  signify  little  as  a  ground  for  infer- 
ence. They  simply  demonstrate  gaps  in  our  knowledge.  (2)  A 
closer  study  shows  that  the  supposed  gaps  are  not  so  wide  as  im- 
agined. The  so  called  Silurian  Fishes  reveal  graduations  down- 
ward toward  Crustaceans  and  Tunicates,  and  upward  toward 
Amphibians.  So  of  all  the  great  salient  types.  They  are  all 
"comprehensive";  and  the  characteristic  of  a  comprehensive 
type  is  to  blend  to  some  extent  with  neighboring  types.  (3)  The 
daily  progress  of  discovery  brings  to  view  types  which  fit  into 
the  existing  gaps.  The  gaps  are  becoming  filled  up.  There  are 
already  long  lines  of  succession  where  the  graduation  from  lower 


FIG.  220. — WEATHERED  SPECIMEN  or  Eozoon  Canadense.    From  Limestone   at  Tudor, 

Ont.     (Carpenter.) 

to  higher  is  as  gentle  and  complete  as  could  be  demanded  to  sup- 
port an  extreme  inference.  The  tenor  of  progress  foreshadows 
the  complete  closing  up  of  the  gaps.  It  shows,  at  least,  that 
they  would  probably  be  filled  if  we  could  recover  the  complete 
record.  It  seems  to  be  more  rational  in  this  day  to  anticipate 
this  result  than  to  attribute  high  significance  to  defects  in  our 
knowledge  which  to-morrow  may  no  longer  exist.  We  may, 
therefore,  reason  from  the  chain  of  organic  being,  as  if  no  links 
were  missing. 

§  3.     The  Dawn  Animal. 

We  will  now  glance  more  particularly  at  some  of  the  domi- 
nant types  of  organization.  In  doing  this,  the  student  should 
make  frequent  reference  to  the  table  of  classification  in  the  sec- 


PROGRESS   OF   TERRESTRIAL   LIFE. 


319 


ond  section  of  this  chapter.  First  of  all  was  Eozoon.  The  re- 
mains of  its  calcareous  skeleton  have  been  found  far  down  in  the 
Laurentian  System,  in  a  great  bed  of  crystalline  limestone.  When 
exposed  on  the  weathered  surface  of  the  rock  it  appears  formed 
of  numerous  bent  or  undulate  layers  parallel  with  each  other,  as 
shown  in  Fig.  220.  These  layers,  in  most  cases,  consist  alter- 
nately of  serpentine  and  calcium  carbonate.  When  a  thin  cross 
section  is  made  and  highly  magnified,  we  are  enabled  to  detect 
a  minute  structure  bearing  considerable  resemblance  to  certain 
Foraminifera.  We  should  wander  too  far  to  enter  into  details 
of  explanation,  and  must  be  content  with  stating  that  Eozoon  is 
generally  regarded  foraminiferal  in  its  affinities. 

We  may,  then,  give  some  account  of  its  structure  and  mode 
of  life.  At  the  beginning  of  its  growth  it  consisted  of  a  small 
mass  of  gelatinous  substance  spread  on  some  support  in  the  bot- 
tom of  the  sea.  It  probably  resembled  the  well  known  Amoeba 
living  in  modern  fresh 
waters,  of  which  one  is 
represented  in  Fig.  221. 
This  is  a  minute  speck 
of  gelatinous  matter  con- 
taining granules,  a  nu- 
cleus, n,  and  a  contractile 
vesicle,  c  v.  Extensions 
from  the  mass  of  the  ani- 
mal's body,  called  pseu- 
dopodia,  are  capable  of 
complete  withdrawal, 
and  fusion  in  the  com- 
mon mass.  Other  pseu- 
dopodia  may  be  extended 
at  the  animal's  pleasure. 
This  minute  creature, 
without  permanent  mem- 
bers,  without  stomach  or 
other  organs,  possesses 


^c  v 


FIG.  221.— Amoeba  Proteus.  (After  Leidy.)  A  LIV- 
ING REPRESENTATIVE  OF  THE  OLDEST  ANIMAL. 
n,  nucleus;  c  v,  contractile  vesicle;  a,  posterior 
portion  in  a  contracted  state;  c,  c,  two  pseudo- 
pods  closing  around  an  Infusorian  (Urocentrum)', 
d,  diatoms  within  the  animal ;  6,  particles  of  saw- 
dust. Magnified  100  diameters  in  the  upper  speci- 
men, and  125  in  the  lower.  Found  frequently  in 
fresh  waters. 


320 


GEOLOGICAL    STUDIES. 


all  the  essentials  of  animal  life.  It  hungers  and  feeds;  it  wills 
and  moves;  it  is  self-conscious  and  seeks  to  satisfy  its  wants. 
This  is  nearly  the  simplest  form  of  organization  known.  (See 
page  30G.)  It  stands  as  a  representative  of  the  oldest  type  of 
animal  existence. 

But  the  first  animal  found  its  home  in  the  stormy  sea.  It 
must  be  sheltered  from  the  violence  which  raged  around  it.  A 
thin,  shelly  covering  was  secreted  over  it.  This  was  perforated 
by  innumerable  minute  tubuli,  and  by  some  larger  pores,  and  was 
supported  at  intervals  by  calcareous  pillars.  Over  this  shell  was 
built  a  thicker  and  coarser  covering,  known  as  the  supplementary 
skeleton.  This  was  perforated  by  branching  canals,  through 
which  the  gelatinous  matter  found  its  way  to  the  exterior.  Here 
new  pseudopods  were  extended,  and  new  gelatinous  matter  was 
outspread,  and  a  new  roof  was  built,  supported,  like  the  first,  by 
numerous  stony  pillars.  This  process  was  repeated  again  and 
again,  and  the  mass  grew  indefinitely.  The  accompanying  dia- 
gram is  intended  to 
illustrate  the  mode  of 
growth  just  described. 
Organisms  of  this  sort 
were  probably  planted 
in  innumerable  places 
along  certain  favorable 

tracts    of    sea   bottom- 
In  the  progress  of  their 

growth  many  coalesced 
together,    and    e  11  o  r  - 

mous   reef-like   masses 

FIG.  222.— DIAGRAM  OF  STRUCTURE  OF  Eozodn.  (Biitsch-  .                                   - 

li,  after  Carpenter.)    K,  Chambers  of  two  successive  came,  111  the    course   of 

layers;  a,  Shelly  partitions,  perforated  by  passages;  of  ages,  into  existence. 

K\  Proper  walls  of  the  chambers,  composed  of  finely  .              ,     ,              ,             , 

tubular  shell  substance— the" nummulinc  layer ";  sK,  Around  these   the   sed- 

Intermediate,  or  supplementary  skeleton,  traversed  by  iments     gathered,     and 

s  t,  stolons  of  communication  between  two  chambers  -,-,      , ,                        •       j        * 

of  different  layers,  and  bye,  a  system  of  canals.  a11     that     remained     ot 

Eo  zo  on  was   buried 
thousands  of  feet  in  rock-forming  mud. 


PROGRESS    OF   TERRESTRIAL    LIFE. 


321 


But,  though  Eozoon  disappeared  from  existence,  the  type  to 
which  it  belonged  survived.  In 
the  Cambrian  we  have  long  known 
a  form  represented  in  Fig.  223, 
and  called  Stromatocerium  rugo- 
sum.  This,  in  external  aspect, 
resembles  Eozoon^  but  its  zoologi- 
cal affinities  remain  somewhat  in 


FIG.  223.  —  Stromatocerium  rugosum. 
FROM  THE  CAMBRIAN  OF  NEW  YORK. 
(After  Hall.) 


question. 

It  will  be  interesting  to  trace 
the  last  named  type  a  little  fur- 
ther. It  is  the  type  of  the  Stro- 
matoporidce.  In  Fig.  224  is  a 
view  of  another  Stromatoporoid. 
The  typical  Stromatopora,  when 
cut  through,  is  seen  to  consist 
(Fig.  225)  of  a  large  number  of 
concentric  laminae,  separated  by 
very  thin  intervals,  and  connected  by  innumerable  pillars  passing 
from  lamina  to  lamina.  This  is  a  simple 
Stromatopora.  Sometimes  the  pillars  be- 
come more  or  less  obscure  (Fig.  226);  some- 
times they  disappear;  sometimes  the  lami- 
nae are  all  raised  at  intervals  into  little 
eminences,  shown  in  Figs.  224  and  227; 
sometimes  small,  radial,  sinuous,  and 
branching  canals  diverge  from  one  or  more 
perforations  in  these  eminences  (Fig.  227); 
and  by  these  and  similar  variations,  we 
find  established  a  number  of  generic  dis- 
tinctions. Stromatocerium  is  a  genus  without  pillars,  and  having 
all  the  laminae  pierced  by  small  holes.  Three  genera,  Stromato- 
pora, Ccenostroma,  and  Idiostroma,  are  extremely  abundant  in 
the  Devonian  limestone  of  Little  Traverse  Bay,  Michigan.  The 
first  is  small,  from  the  size  of  a  hickory  nut  to  that  of  one's  fist. 
The  second  grows  in  huge  dome-shaped  masses,  some  of  which 


FIG.  224.— VIEW  or  A  STRO- 
MATOPOROID, Stromatopo- 
ra tuberculata  (Nichol- 
son). FROM  CORNIFEROUS 
LIMESTONE. 


322 


GEOLOGICAL   STUDIES. 


have  been  measured  over  twelve  feet  across,  and  recall  the  reef- 
like  bulk  of  long  extinct  Eozoon. 
The  third  genus  is  an  enormous 
tangled  mass  of  branching  stems, 
each  a  third  of  an  inch  in  diame- 
ter, and  having  a  true  stromatopo- 
roid  structure.  Stromatoporoids 
are  widely  distributed  through  the 
Devonian,  and  they  are  also  com- 
mon in  the  Silurian.  Their  near- 
est affinities  are  yet  undecided. 
They  have  by  different  authorities 
been  referred  to  the  Foraminifera, 
the  Sponges,  the  Anthozoa,  the 
Hydrozoa,  and  the  Polyzoa.  Probably  they  must  be  considered 
one  of  the  comprehensive  types  (described  on  page  316),  which 
cannot  be  assigned  precisely  to  any  recognized  position. 


FIG.  225.— INTERNAL  STRUCTURE  OP 
Sfromatopora  stnatella  D'  ORB.  x  7. 
(From  Nature.) 


FIG.  226.— VERTICAL  SECTION  THROUGH 
Ccenostroma  monticuliferum.  (From 
Nature.)  SHOWING  OBSCURE  LAMINA 
AND  PILLARS. 


FIG.  227. — EXTERIOR  or  C&nostrotna  mon- 
ticuliferum. X  2.  (From  Nature.) 
SHOWING  MONTICULES  AND  RADIAL 
CANALS. 


The  type  of  Foraminifera,  of  which  Eozoijn  and  the  Stroma- 
toporoids combined  some  of  the  characteristic  features,  became, 
in  later  times,  completely  eliminated,  and  underwent,  during 
Mesozoic  and  Caenozoic  times,  a  remarkable  diversification.  It 
survives  to-day  in  a  large  number  of  representatives. 

Eozoon  played  the  first  role  in  the  drama  of  life.  It  was  the 
great  lime-secreting  and  reef-building  agent  of  the  early  ages  of 


PROGRESS    OF   TERRESTRIAL   LIFE. 


323 


the  world.     Later,  this  function  was  assumed  by  organisms  of 
another  and  higher  class. 

§  4,      Trilobites. 

At  the  very  opening  of  the  Cambrian  Age,  Trilobites  were 
present.  Their  advent  and  reign  form  a  striking  feature  in  the 
history  of  life.  Some  of  their  forms  are  shown  in  Figs.  228-230. 
They  were  Arthropoda,  holding  a  position  low  in  the  Class 


Niagarensis.  FROM 
NIAGARA  GROUP. 


FIG.    228,—Paradoxides  Harlani.      (After 
Walcott.)    FROM  EARLY  CAMBRIAN. 


FIG.  230.— SAME  AS 
LAST,  ROLLED  TO- 
GETHER. 


Crustacea.  The  body  was  distinctly  trilobed.  The  anterior  por- 
tion constituted  a  cephalic  shield,  usually  bearing  a  pair  of  ses- 
sile compound  eyes,  with  a  raised,  often  lobed  (Fig.  229)  central 
part,  known  as  glabetta.  The  number  of  thoracic  segments  was 
very  variable.  The  abdominal  segments  were  firmly  united,  and 
formed  a  caudal  shield.  Fig.  231  is  a  diagram  showing  the  prin- 
cipal parts  of  a  Trilobite,  as  seen  from  above. 


324 


GEOLOGICAL   STUDIES. 


Some  of  the  lowest  Cambrian  strata 
are  crowded  with  the  fragments  of  these 
articulates.  They  continued  abundant 
during  the  Silurian;  diminished  during 
the  Devonian,  and  became  extinct  dur- 
ing the  Carboniferous.  Their  nearest 
living  representative  is  the  King  Crab 
(Limulus)  of  our  eastern  coast,  the 
embryo  of  which  presents  a  strikingly 
trilobitic  aspect. 

FIG.  231.--DIAGRAM  or  THE  STRUCTURE  OF  A  TRI- 

LOBITE. 

A,  HEAD.  1,  External  Border  of  the  Limb.  2,  Mar- 
ginal Furrow.  3,  Occipital  Ring.  4,  Glabella.  5, 
Great  Suture,  passing  in  front  of  the  Glabella,  and 
inside  of  the  Eyes.  6,  Eyes  and  Subocular  Suture,  a,  Fixed  Cheek,  forming  along 
side  of  the  Eye,  the  Palpebral  Lobe,  a  5.  6,  Movable  Cheek,  g,  Genal  Point. 

B,  THORAX.     7,  Ring  of  the  Axis  of  each  Segment  of  the  Thorax.    8,  Rib  of  each  Seg- 
ment of  the  Thorax. 

C,  PYGIDIUM.    9,  Continuation  of  the  Axis.    10,  Continuation  of  the  Ribs. 

§  5.     Crinoids. 

A  crinoid  consists  of  body  and  arms,  sup- 
ported on  a  stem,  which  is  generally  rooted  in 
the  submarine  soil.  It  presents  the  appear- 
ance of  a  tree,  and  hence  is  embraced  in 
the  group  formerly  known  as  zoophytes  (Fig. 
232).  The  parts  mentioned  are  composed  of 
calcium  carbonate,  and  each  consists  of  a  num- 
ber of  pieces  nicely  fitted  together.  The  stem 
is  a  pile  of  circular  or  pentagonal  discs,  with  a 
central  canal  extending  the  whole  length.  The 
calyx,  or  cup,  consists  of  regularly  shaped  plates 
fitted  by  their  edges.  The  arms,  five  in  number, 
are  ranges  of  discoid,  or  imperfectly  cylindrical 
pieces,  in  one  or  two  series,  joined  by  their  flat- 
tened surfaces,  but  not,  like  the  stem,  perforated 
for  a  canal.  The  arms  generally  bifurcate  near 
the  base,  and  afterward  again.  From  one  or  both 


FIG.  232.—  Rhizocri- 
nus  Lofotensis. 
(After  W.  Thom- 
son.) A  LIVING 
CRINOID.  X  2. 


PROGRESS   OF   TERRESTRIAL   LIFE. 


325 


sides  of  each  arm  generally  spring  pinnulse,  constructed  like 
the  arms,  but  smaller.  Over  the  calyx,  in  the  extinct  spe- 
cies, is  generally  built,  of  nicely  fitting  plates,  a  dome  bearing  the 
passages  to  and  from  the  interior.  Sometimes  one  of  these  opens 
at  the  apex  of  a  proboscis  which  rises  from  the  dome.  The  plates 
of  the  calyx  are  often  elegantly 
furrowed  or  sculptured.  Their 
forms,  number  and  arrangement 
are  shown  in  Fig.  233,  which 
represents  the  plates  of  a  calyx 
spread  out  horizontally.  They 
are  grouped  as  Basal,  Itadial, 
Interradial,  and  Azygos  plates. 
The  basal,  b,  b,  b,  consist  gen- 
erally of  a  cycle  of  three  plates 
resting  on  the  top  of  the  stem. 
Frequently,  however,  there  are 
two  cycles  of  basals.  Whether 
of  one  or  two  cycles,  the  basals  FIG 
are  surmounted  by  five  series  of 
radials,  r.  Each  series  consists 
of  the  primary,  secondary,  and 
(sometimes)  ternary,  radials 
(r\  r2,  r3).  Between  the  radi- 
als are  interradials  (i1,  i*,  £8), 
which  generally  exist  in  two  or  more  cycles,  having  a  definite 
number  between  each  two  series  of  radials,  except  on  one  side, 
called  the  azygos  interradius,  where  the  number  is  much  greater 
(a1,  «2,  etc.).  It  will  be  seen  that  the  principle  of  bilaterality  is 
fully  exemplified  in  this  arrangement.  A  line  drawn  from  the 
azygos  side  through  the  centre  of  the  opposite  radial  series  divides 
the  structure  into  right  and  left  parts,  perfectly  symmetrical  with 
each  other. 

These  elaborately  constituted  organisms  were  in  existence  in 
the  Cambrian  Age.  The  type  underwent  expansion  in  number 
and  elaborateness  through  the  Silurian,  continued  through  the 


—  CALYX  or  A  CRINOID,  SPREAD 
OUT  TO  SHOW  THE  FORMS,  NUMBER,  AND 
ARRANGEMENT  OF  THE  PLATES.  6,  6,  &, 
Basal  Plates,  ri,  r2,  r-3,  Radials.  i  r,  In- 
terradials. oi,  a2,  Azygos  Interradials. 
There  are  here  three  radials  in  each  radius ; 
four  interradii,  each  with  five  interradials, 
and  one  azygos  interradius,  with  a  larger 
number  of  pieces. 


326  GEOLOGICAL   STUDIES. 

Devonian,  and  attained  its  greatest  de- 
velopment in  the  Lower  Carboniferous. 
Certain  genera  lived  through  the  Meso- 
zoic;  but  the  type  at  the  beginning  of 
the  Tertiary  was  nearly  extinct.  Till 
recently,  but  one  living  species  was 
known.  Now,  however,  a  number  of 
additional  species  have  been  dredged, 
mostly  from  the  Gulf  Stream,  off  the 
coasts  of  Florida  and  Scandinavia,  the 
late  Challenger  Report  enumerating  six 
genera  and  thirty-two  species.  It  is  a 
very  remarkable  circumstance  that 
among  the  genera  represented  is  Rhiz- 
oc'rinus,  Fig.  232,  which  began  its 
CARBONIFEROUS  existence  in  the  Cambrian  Age.  In  the 
CRINOID,  Forbesiocrinus  com-  cold  depths  of  the  ocean,  changes  of 
m«ni.,WAVEBLY  GROUP,  OH:O.  conditions  are  glight>  and  slow>  We 

judge  that  the   modern  conditions  have  persisted   substantially 
from  the  dawn  of  crinoidal  life. 

§  6.     Chambered  Shells. 

Another  of  the  conspicuous  types  of  organization  of  which 
the  elementary  student  should  have  some  knowledge  is  that  of 
Tetrabran'chiate  Ceph'alopods.  These  molluscs  secreted  an  ex- 
ternal calcareous  shell,  in  form  a  hollow,  tapering  cone,  straight 
or  bent,  and  divided  at  intervals  by  transverse  partitions  called 
septa.  The  intervening  spaces  are  chambers,  and  the  last  one  is 
occupied  by  the  animal,  as  shown  in  cut,  Fig.  235.  The  animal  — 
to  judge  from  the  Nautilus,  the  only  living  genus  —  was  fur- 
nished with  many  flexible  prehensile  tentacles,  or  arms,  well 
developed  eyes,  a  pair  of  horny  mandibles,  two  pairs  of  plume- 
like  gills,  a  funnel,  for  expulsion  of  respired  water,  and  a  si- 
phuncle,  consisting  of  a  membranous  or  calcareous  tube,  which 
reached  from  the  posterior  part  of  the  body  through  all  the  septa 
and  chambers.  The  siphuncle,  in  some  families,  passed  through 


PROGRESS   OF   TERRESTRIAL   LIFE. 


327 


the  centre  of  the  shell,  or  near  it;  in  others  it  was  closely  mar- 
ginal on  one  side  or  the  other  (dorsal  or  ventral).  See  the 
upper  row  of  outlines  in  Fig.  236. 


FIG.  235.— RESTORATION  OF  AN  Orthoceras  —  A.  STRAIGHT,  CHAMBERED  SHELL,  or  PALAE- 
OZOIC TIME,    a,  arms;  /,  funnel;  c,  chamber;  s,  siphuncle. 

The  septum  was  sometimes  simply  concave,  as  at  e;  and  in 
this  case  the  siphuncle  was  central,  or  sub-central.  Sometimes 
the  suture,  or  line  of  junction  with  the  shell,  was  broadly  undu- 
late, and  the  siphuncle  was  on  the  inner  side,  as  at  d.  Some- 
times, with  siphuncle  close  to  the  outer  margin,  the  suture  was 


FIG.  236.— POSITION  OP  SIPHUNCLE  AND  FORM  or  SEPTA  IN  VARIOUS  TETR ABRANCHIATE 
CEPHALOPODS.  The  upper  row  of  figures  represents  transverse  sections  of  the  shells; 
the  lower  row  the  edges  of  the  septa,  a,  a,  Ammonites  ;  6,  &,  Ceratites  ;  c,  e,  Gonia- 
tites  ;  d,  d,  Clymenia  ;  e,  e,  Nautilus,  or  Orthoceras. 

simply  lobed  (curved  or  angulate),  as  at  c;  or,  with  the  lobe 
denticulated,  as  at  b  ;  or,  with  the  lobes  lobulate  and  denticulate 
(often  called  foliated],  as  at  a. 

The  five  different  styles  represent  degrees  of  complication. 
According,  therefore,  to  the  method  of  nature  (page  315),  the 
simplest  styles  are  the  more  ancient,  and  began  to  exist  in  the 


328  GEOLOGICAL   STUDIES. 

Cambrian.  In  the  Cambian  and  Silurian  the  type  underwent  its 
greatest  development,  though  it  still  survives  in  Nautilus.  The 
angulated  septum  belongs  to  the  Devonian;  the  lobed  septum,  to 
the  Carboniferous,  though  it  began  in  the  Devonian;  the  denticu- 
late-lobed  septum  characterizes  the  Triassic,  and  the  foliated 
septum  is  known  only  in  the  middle  and  later  Mesozoic. 

Again,  these  chambered  shells  exhibit  all  degrees  of  enrol- 
ment, from  straight  to  closely  coiled.  These  variations  may  be 
advantageously  set  forth  by  means  of  the  scheme  on  the  follow- 
ing page.  Here  we  have,  first,  an  analysis  of  the  form,  and  op- 
posite this,  in  two  columns,  the  names  of  genera  possessing  the 
several  forms.  In  the  first  column  are  generic  names  of  Nautil- 
oidea,  and  in  the  next  names  of  Ammonoidea.  The  names  of 
Nautiloidea  which  stand  a  little  indented  are  of  the  type  having 
a  contracted  aperture;  and  the  names  of  Ammonoidea  which 
stand  a  little  indented  are  of  the  Ceratites  type,  having  the 
lobes  denticulated.  We  witness  in  this  table  an  interesting  ex- 
emplification of  nature's  tendency  to  permutation  of  characters, 
or  repetitions  of  characters  of  second  order  under  each  of  the 
characters  of  first  order. 

The  Tetrabranchs  are  divided  into  Nautiloidea  and  Ammo- 
noidea, the  former  having  the  suture  simple  and  the  siphuncle 
central  or  sub-central;  and  the  latter  having  the  suture  lobed  or 
foliated,  and  the  siphuncle  mostly  close  on  the  ventral  (external) 
margin.  Of  the  Nautiloidea  the  three  most  important  families 
are  the  OrtJiocerat' idee,  having  the  shell  straight  (Figs.  235,  237); 
the  Cyrtoceratidce,  having  the  rapidly  tapering  shell  strongly 
bent  (Fig.  238),  and  the  Nautilidce^  having  the  shell  coiled  in 
a  plane  (Fig.  239).  The  Orthoceratidce  underwent  an  extraor- 
dinary development  during  the  Cambrian  and  Silurian  —  some- 
times attaining  a  length  of  fifteen  feet  —  and  were  abundant 
during  the  Devonian.  During  all  the  Carboniferous  they  were 
on  the  wane,  and  are  not  known  later,  except  as  a  local  develop- 
ment in  the  Trias.  The  Nautilidm  appeared  at  the  beginning 
of  the  Silurian,  became  plentiful  in  the  Carboniferous,  and  the 
genus  Nautilus  still  survives. 


PROGRESS    OF   TERRESTRIAL    LIFE. 


329 


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330 


GEOLOGICAL    STUDIES. 


The  Ammonoidea  were  mostly  Mesozoic,  and   underwent  -a 
remarkable  development  in  respect  to  diversification  and  num- 


FIG.  237.— Orthoc'eras  Carleyi,  Devonian,  Ohio. 
FIG.  %®,.—Cyrtoc'eras  Eugenium,  Corniferons,  New  York. 
FIG.   239.— Gyroc'eras  undula'tum,  Corniferous,  Cherry  Valley, 
N.T. 

bers.     The    Ctymenidce,  with  internal    (dorsal) 
siphuncle  and  angulated  suture   lines,  were  re- 
stricted to  the  Devonian,  and  never  became  numerous.     The  G-o- 

niatitidoB  were  more  im- 
portant. They  had  a 
closely  ventral  (exter- 
nal) siphuncle,  and  a 
suture  line  bent  into 
lobes  and  saddles  (for- 
ward pointing  and  back- 
ward pointing  lobes). 
They  made  their  advent 
in  the  Devonian  and  be- 
FIG.  240.—  Ammoni'tes  serpenti'nus.  a,  side  view;  6,  came  an  important  type 


edgewise  view;  c,  plan  of  suture-lobes.  .  , 

Since  the  Palaeozoic  they  have  been  extinct. 


Carboniferous. 


PROGRESS    OF   TERRESTRIAL    LIFE.  331 

§  7.     Fishes. 

The  earliest  vertebrates  were  fish-like,  and  we  commonly 
group  them  with  Fishes;  but  probably,  if  their  characters  were 
completely  known,  we  should  feel  constrained  to  establish  one  or 
more  separate  classes  for  their  reception.  TELEOSTEI,  or  ordi- 
nary fishes,  have  the  skeleton  completely  ossified;  but  sturgeons 
and  sharks  have  an  imperfectly  ossified  skeleton.  The  earliest 
fishes  appear  to  be  somewhat  allied  to  these,  and  they  are  com- 
monly arranged  under  two  orders:  GANOIDEI,  having  the  exo- 
skeleton  (or  bony  developments  of  the  surface)  in  the  ganoid 
scales,  plates  or  spines,  and  ELASMOBRANCHII,  including  Sharks, 
Rays,  and  Chimcerce,  having  the  exoskeleton  placoid — consist- 
ing of  grains  or  tubercles.  The  Ganoidei  are  subdivided  into 


FIG.   241.— RESTORATION   OF   Dinich'thys   Herz'eri,   A   PLATED   GANOID   FKOM    OHIO. 

(Newberry). 

Lepidoganoids  (scale-covered)  and  Placoganoids  (plate-bearing). 
The  last  embrace  the  Sturgeons,  which  are  modern,  and  the  Pla- 
coderms,  which  are  one  of  the  oldest  types  of  fishes.  Until  lately 
the  oldest  known  American  fishes  were  Devonian,  though  a  Silu- 
rian fish-bed  has  long  been  known  in  England.  In  1884,  how- 
ever, Professor  Claypole  announced  the  discovery  of  American 
fishes  in  the  middle  Silurian  of  Pennsylvania;  that  is,  as  low  as 
the  bottom  of  the  Salina  Group;  while  the  oldest  European  fishes 
are  supposed  to  be  of  the  age  of  the  Helderberg  Group.  The 
name  of  the  oldest  fish  known  is  Pakeas'pis,  "ancient  shield." 
Indications,  however,  are  found  of  still  older  fishes  in  the  Clinton 
sub-group,  and  named  On'chus  Clintoni.  This  group  probably 
corresponds  to  the  Upper  Llandovery  of  England. 


332 


GEOLOGICAL   STUDIES. 


The  oldest  well  preserved  Placoderms  in  America  come  from 
the  Devonian  Huron  Shale  of  Ohio,  and  have  been  described  by 
Dr.  Newberry.  One  of  these  is  named  Dinich'thys,  or  "  terrible 
fish."  D.  Herzeri  appears  to  have  attained  a  length  of  at  least 
twenty  feet.  Its  head  was  three  feet  long  and  two  broad,  and 
the  under  jaws  were  two  feet  long.  A  restoration  of  this  species 
is  shown  in  Fig.  241.  The  tail,  it  will  be  noticed,  like  that  of 
most  Palaeozoic  fishes,  was  heterocercal,  or  "unequal-lobed."  In 
the  Devonian  flourished  also  huge  Lepidoganoids.  One  of  the 
Ohio  species  is  named  Onych'odus  sigmoi'des  by  Newberry. 
The  skeleton  was  cartilaginous,  but  .  the 
teeth  were  long  and  formidable.  A  group 
of  these  is  shown  in  Fig.  242.  It  had  jaws 
twrelve  to  eighteen  inches  long,  and  proba- 
bly attained  a  length  of  twelve  to  fifteen 
feet.  Besides  Ganoids,  there  were  huge 
Elasmobranchs  of  the  sub-order  Plag'io- 
stomes,  which  includes  modern  Sharks  and 
Rays,  and  the  type  of  ancient  or  Cestraciont 
Sharks,  some  of  which  still  live  in  Austra- 
lian seas.  The  back  teeth  in  the  latter  were 
obtuse,  and  there  was  a  powerful  spine  in 
front  of  each  dorsal  fin.  Fig.  243  shows  one 
of  these  spines  from  New  York,  which, 
when  perfect,  was  as  least  ten  inches  long.  The  Cestrac'ionts 


FIG.  242.— GROUP  OF 
FRONT  TEETH  OF 
Onych'odus  sigmoides, 
A  SCALED  GANOID  FROM 
THE  CORNIFEROTJS  OF 
OHIO.  (Newberry.) 


FIG.  243.— SPINE  OF  AN  EXTINCT  CESTRACIONT  SHARK.  Machceracan'thus  sulcatus.  (After 

Hall.) 

and  still  another  group,  Hyb'odonts,  more    resembling   modern 
Sharks,  became  abundant  during  the  Mesozoic  ages. 

In    Europe,    the  Pterich'thys  or  "Winged  Fish,"  Fig.  244, 
has  been  long  a  familiar  form.     This  was  a  companion  of  Ceph- 


PROGRESS    OF   TERRESTRIAL    LIFE. 


333 


alas' pis,    "Shield    Head"   and  Cocos'teus,    "Berry    Bone/'  and 
several  others. 

From    Canada,     at     Scammenac 
Bay,    Mr.     Whiteaves    described    a 
Pterich'thys   Canadensis,  Fig.   247. 
It    has,    however,    no    tail,    and   the 
sculpturing  of  the   plates   resembles 
JBothriol '  epis,  of  which  species  are 
known  in  Europe,  and  in  the  Cats- 
kill  Group  of  America.     Cope  points 
out  some  remarkable    affinities  with 
an  Arctic  Tunicate,  Fig.  248,  and  in- 
fers that  the  Pteriehthy'idw  are  not  FlG>  ^_PleriCMhys  miieri,  FROM 
a  distant  remove  from  an   ancestral      THE    DEVONIAN    OP    SCOTLAND. 
type  of  Tunicates.      From  the  same      (Afte 
locality  are  described  other  fish  remains,  among  them  a  Phanero- 


FIG.  245.—  Gephalas'pls  Lyelll.     (After  Brown.) 


pleuron,  a  near  relative  of  the  living  Queensland  Cerat'odus,  and 
species  of  the  genera  Diplacari 'thus,  Acantho'  des,  Eusthenop'  - 


FIG.  246.—  Coccos'teus  decip'iens.    (After  Jukes.) 

teron,     Glyptol' epis,     Cheirol' epis,    Coccos'teus,    Cephalas'pis, 
Ctenacari  thus,  and  Homacan' thus. 

The  types  to  which  these  Placoderms    and  Cestracionts  be- 


334 


GEOLOGICAL   STUDIES. 


longed  passed  mostly  out  of   existence   during  Palaeozoic  time. 

The  Lepidoganoids  and  ordinary 
Sharks  continued  to  nourish  dur- 
ing   the    Carboniferous   and  the 
Mesozoic.     Teleost  Fishes  began 
to  appear  in  the 
Jurassic,  but  only 
became  abundant 
in  the  Cretaceous 
and    later    ages. 
They  remain  the 
dominant 
of   fishes 

so'ma  Maclovia'-    though  a  slender 
representation  of 
some  of  the  older 
types     still    sur- 
The  corn- 
gar     pike, 


type 


FIG.    m 


FIG.  IW.—  Bothriolepis  Canadensis,  Whit- 
eaves  sp.  VIEWED  FROM  ABOVE.  HALF 
SIZE  OF  A  SMALL  SPECIMEN  (Cope).  FROM 
THE  UPPER  DEVONIAN. 


ERED   TUNICATE 

FROM  POINT  BAR- 

R  o  w,     ALASKA. 

To    ILLUSTRATE    Vives. 

AFFINITY    WITH 

Pterichthyidce. 


mon 

Lepidosteus,  is 
well  known  in  our  western  and  southern  fresh  waters.  It  has 
acquired,  however,  a  bony  skeleton,  and  the  tail  is  less  hetero- 
cercal  than  that  of  the  allied  ancient  species. 


FIG.  249. — Lepidosteus  Huronesis,  THE  LAKE  GAR  PIKE.    LIVING  IN  THE  GREAT  LAKES. 

(From  Nature.) 
FIG.  -250.—  Lepidosteus  oculatus,  THE  SPOTTED  GAR  PIKE.    LIVING  IN  LAKE  ERIE  AND 

SOME  SMALL  LAKES  OF  MICHIGAN.     (From  Nature.) 

It  will  be  remarked  that  the  ancient  types  of  fishes  possessed 
in  some  respects,  an  embryonic  character.  Their  skeletons  were 
cartilaginous  like  those  of  the  embryos  of  Teleosts,  and  their 


PROGRESS    OF   TERRESTRIAL    LIFE.  335 

tails  are  heterocercal  or  even  vertebrated.  The  tendency  of  the 
embryo  tail  to  a  vertebrate  structure  and  hence  to  a  heterocercal 
character  may  be  well  seen  in  the  embryo  of  Lepidosteus,  a 


7/ainch 

FIG.  251.— EMBRYO  OF  Lepidosteus  PROM  THE  CUMBERLAND  RIVER,  NASHVILLE,  TEN- 
NESSEE, SHOWING  A  VERTEBRATE  TAIL.    (From  Nature.) 

representation  of  which  is  given  in  Fig.  251.  This  correspond- 
ence between  embryos  of  modern  types  and  the  adults  of  ancient 
types  is  a  general  principle  in  the  history  of  life. 

To  the  period  of  the  Coal  Measures,  Fishes  were  the  highest 
type  of  animals  in  existence.  As  in  the  early  history  of  other 
types,  they  were  also  numerous  and  bulky.  For  these  reasons 
palaeontologists  have  designated  the  Devonian  and  Carboniferous 
the  "  Reign  of  Fishes." 

§  8.     Reptiles. 

Reptiles  are  essentially  a  post-Palaaozoic  type.  Telerpeton  and 
Stagonolepis  have  been  reported  from  the  Elgin  sandstones  of 
Scotland,  and  these  have  been  regarded  as  Devonian,  but  they 
may  with  great  probability  be  referred  to  the  Trias.  It  is  thought 
also  that  Eosaurus  Acadiensis,  a  vertebra  of  which  was  found 
by  Marsh  in  the  Nova  Scotia  Coal  Measures,  may  have  been  a 
"marine  saurian."  Generally  the  place  of  Reptiles  was  taken  in 
the  Coal  Measures  by  Labyrinthodonts,  an  Order  of  Amphibians. 
Possibly,  however,  the  little  Hylonomus  was  a  true  reptile.  In 
the  Permian,  the  last  group  of  Palaeozoic  strata,  occur  in  Europe 
the  remains  of  Protorosaurus,  a  lizard-like  reptile,  together  with 
other  forms. 

But  the  Mesozoic  was  the  theatre  of  the  chief  development 
of  Reptiles.  Not  only  were  they  numerous  and  often  gigantic  in 
dimensions,  but  many  were  heavily  armored;  and  the  type,  while 
its  forms  were  comprehensive,  became  wonderfully  differentiated, 


336 


GEOLOGICAL   STUDIES. 


so  that  reptilian  life  became  fitted  to  inhabit  all  elements,  and 
utilize  all  conditions  of  existence. 


FIG.  252.— Ichthyosaurus  communis.    (D'Orbigny.) 

The  sea  had  its  reptilian  denizens — Ichthyosauria,  fish-like  in 
their  home,  their  form,  their  structure.  The  head  of  the  common 
Ichthyosaurus,  Fig.  252,  was  enormous,  with 
a  huge  snout  ;  neck  wanting  ;  teeth  conical, 
strong,  and  numerous;  orbits  of  immense  size; 
a  long  series  of  ribs  extending  from  the  neck 
to  the  elongate  tail;  sternum  and  sacrum 
wanting;  vertebras  bi-concave;  all  the  limbs 
paddle-like,  composed  each  of  numerous  short 
polygonal  bones  arranged  generally  in  five 
longitudinal  rows,  with  a  supernumerary  row 
of  ossicles  on  each  side,  giving  the  appear- 
ance of  seven  digits,  each  with  many  pha- 
langes. Species  of  Ichthyosaurus  range 
through  the  Jurassic  and  Cretaceous  of  the 
Old  World. 

In  America  are  found  the  remains  of 
great  reptiles  related  to  Ichthyosaurus,  but 
without  teeth.  They  attained  a  length  of 
eight  or  nine  feet.  The  genus  Baptan' odon^ 
"toothless  bather,"  and  the  Order  BAPTANO- 
DON'TA  have  been  established  for  them  by 
Marsh.  Fig.  253  illustrates  the  foot  of  Bap- 
tanodon  discus.  Here  were  six  digits. 

The   student  will   notice  particularly  the 
primitive  or  low   condition  of    the  limbs   of 
these  Ichthyosauroids.     Each  limb  was  a  simple  fin  or  paddle; 


FIG.  253.— LEFT  HIND 
FOOT  OF  Baptanodon 
discus,  SEEN  FROM 
BELOW.  X  1-10.  F, 
femur;  F',  fibula;  i, 
intermedium;  c,  cen- 
tral bone ;  /,  fibulare ; 
m.  metatarsals;  T, 
tibia;  t,  tibiale.  Ro- 
man numerals  indi- 
cate the  digits  in  or- 
der. (Marsh.) 


PROGRESS    OF   TERRESTRIAL    LIFE. 


337 


FIG.  'HZA.—Plesiosaurus  dolichodei'rus. 
(D'Orbigny.) 


the  fore  and  hind  limbs  were  identical  in  structure;  three  bones 
in  the  second  segment  of  the  limb  (as  tibia,  fibula,  and  inter- 
medium, in  the  hind  limb); 
the  mesopodial  bones  (car- 
pals  or  tarsals)  simple  cir- 
cular or  angularly  rounded 
discs;  the  number  of  digits 
six  or  more;  the  metapo- 
dial  bones  (rnetacarpals  and 
metatarsals)  and  also  the 
phalanges,  mere  circular 
discs,  and  the  phalanges 
very  numerous.  These 
limb-characters,  like  the  general  features  of  Ichthyosaurus  be- 
fore enumerated,  point  clearly  to  a  close  relationship  with  preex- 
isting and  contemporary  fishes.  The  thoughtful  biologist  cannot 
avoid  the  question  how  such  affinities  came  into  existence. 

The  PLESIOSAURIA  were  other  sea  monsters.  The  Plesi- 
osaur'us  resembled 
the  Ichthyosaurus, 
but  differed  remark- 
ably in  its  long  neck 
and  snake-like  head. 
A  sacrum  of  two  ver- 
tebrae was  present, 
and  supernumerary 
digits  were  wanting. 
It  attained  a  length 
of  18  to  20  feet,  and 
ranged  through  the 
Jurassic  and  Creta- 
ceous. Elasmosau- 
ru&  platyurus  of  Cope 
attained  a  length  of 
50  feet  (Fig.  255).  Other  marine  saurians  belong  to  the  order 
PYTHONOMOR'PHA,  "sea  serpents,"  of  which  over  fo^ty  American 


FIG.  255.—£}lasmosaurus  platyu'rus.    (Cope.) 


338 


GEOLOGICAL   STUDIES. 


Cretaceous  species  are  known  —  fifteen  in  New  Jersey,  six  or 
more  in  the  Gulf  States,  and  over  twenty  in  western  Kansas. 
Mosasaurus  princeps,  Marsh,  was  75  to  80  feet  in  length.  The 
body  was  covered  with  overlapping  bony  plates.  Each  of  the 
four  paddles  had  five  digits,  but  with  supernumerary  phalanges, 
like  whales.  Besides  conical  saurian  teeth  in  the  jaws,  there 


FIG.  256.— EIGHT  PADDLE  or  Lestosaurus  Mic'romus.     X  1-12. 

were  two  rows  of  formidable  teeth  along  the  roof  of  the  mouth, 
adapted,  as  in  snakes,  for  seizing  their  prey.  To  give  lateral 
motion  to  the  jaws,  an  exceptional  joint  existed  in  front  of 
the  usual  articulation,  and,  as  in  serpents,  the  two  branches  of 
the  lower  jaw  were  unconsolidated  in  front.  The  structures  for 
swallowing  presented,  therefore,  a  truly  snake-like  aspect.  Our 
modern  snakes  appear  to  be  dwarfed  representatives  of  the 
ancient  Mosasaurs,  still  retaining  much  of  their  ancient  fondness 
for  the  water. 


FIG.  257.— KESTORED  JAW  or  Edestosaurus  dispar.    x  1-6. 

The  land  also  had  its  reptilian  denizens.  Of  these,  the  DINO- 
SAIIKIA  are  by  far  the  most  interesting.  Though  commonly 
regarded  as  an  Order,  the  number  of  modifications  of  the  type 
has  been  found  so  great  and  so  extreme  that  Marsh  proposes  to 
regard  the  group  as  a  Sub-Class.  In  one  of  the  Orders,  SAU- 
ROP'ODA  (Lizard-footed),  the  Jurassic  Atlantosaurus  immanis 


PROGRESS    OF   TERRESTRIAL    LIFE. 


339 


attained  the  remarkable  length  of  one  hundred  feet.  The  femur 
was  over  eight  feet  long.  Its  remains  occur  in  Colorado.  The 
related  Morosaurus  grandis  was  40  feet  long.  Apatosaurus 
Ajax  had  the  vertebras  of  the  neck  four  feet  broad,  with  a  sacrum 
of  three  united  vertebrae.  In  another  Order,  ORNITHOP'ODA 
(Bird-footed),  with  only  three  toes  behind,  the  structure  was 
strikingly  bird-like.  Among  these,  Laosaurus  altus  was  about 
ten  feet  long,  and  Nanosaurus  was  quite  diminutive.  In  the 


FIG.  258.—  ffadrosaurus  Foulki, 
A  BIPEDAL  REPTILE  FROM  THE 
CRETACEOUS.  (After  Hawkins1 
Restoration.) 


FIG.  ZSQ.—Iguanodon  Bernissarten'sis,  BOULANGER,  AS 
MOUNTED  IN  THE  MUSEUM  AT  BRUSSELS  BY  DE  PAUW. 
Head,  a,  nostril ;  6,  orbit;  c,  temporal  fossa.  Verte- 
bral column,  d,  cervical  region;  «,  doreo-lumbar  re- 
gion ;  /,  sacral  region ;  g,  caudal  region ;  A,  scapula ; 
i,  coracoid;  £,  hnmerus;  I,  ulna;  m,  radius;  w,  ster- 
num; 0,  ilium;  p,  pubis;  q,  post-pubis;  r,  ischium; 
s,  femur;  t,  tibia;  u,  fibula;  v,  third  (fourth)  trochan- 
ter;  I,  II,  III,  IV,  V,  digits;  X,  diagrammatic  trans- 
verse section  of  the  body  between  the  fore  and  hind 
limbs. 


Cretaceous  beds  of  New  Jersey  are  found  the  remains  of 
Hadrosanrus  Foulki^  a  representative  of  another  family  of  the 
bird-footed  saurians.  This  is  believed  to  have  been  capable  of 
locomotion  on  its  hind  feet,  or,  at  least,  to  have  frequently  sup- 
ported itself  on  two  feet  while  reaching  with  its  fore  feet  to 
gather  its  vegetable  diet  from  the  foliage  of  the  forest.  Three- 
toed  footprints  of  some  bipedal  animals  imprinted  on  the  sand- 
stones of  the  Connecticut  valley  are,  with  much  probability, 


340 


GEOLOGICAL   STUDIES. 


ascribed  to  some  reptile  allied  to  Hadrosaurus.  Ornithotarsus 
immanis  of  Cope,  from  the  shore  of  Raritan  Bay,  was  a  colossal 
Dinosaur,  whose  hind  limb,  according  to  Cope,  could  not  have 
been  less  than  13  feet  in  length. 

In  the  Old  World,  the  Ornithopoda  were  extensively  repre- 
sented by  species  of  Iguanodon.  A  bed  of  their  remains  has  re- 
cently been  brought  to  light  at  Bernissart,  in  Belgium,  and  the 
settled  conclusion  of  M.  Dollo  is  that  Iguan'  odon  was  to  some 
extent  a  bipedal  walker.  Fig.  259  represents  I.  Bernissartensis 
as  recently  mounted  at  Brussels.  The  head  is  14  feet  above 


FIG.  260.— REPTILES  or  MESOZOIC  TIME.    The  upper  and  middle  figures  are  Iguanodon, 
after  Hawkins.    The  right  hand  figure  is  Hylceosaurus. 

the  floor,  and  the  floor  space  covered  is  23  feet  9  inches,  the 
whole  length  of  the  animal  being  over  28  feet.  The  Iguanodon 
was  an  inhabitant  of  fresh-water  marshes,  and  fed  largely  on 
ferns.  It  was  a  powerful  swimmer,  and  there  are  some  indica- 
tions that  the  toes  were  webbed.  Some  years  ago  a  restoration 
of  Iguanodon  was  made  by  Hawkins,  under  the  direction  of  Owen, 
of  London,  and  Fig.  260  gives  the  conception  of  the  reptiles  then 
extant.  But  it  obviously  requires  some  modifications. 

Other,  and  more  characteristically  land  saurians,  constitute 
the  Order  THEEIODONTA,  or  "  Beast-toothed  "  saurians,  from  the 
Triassic  of  South  Africa.  Three  sorts  of  teeth  were  present, 


PROGRESS    OF   TERRESTRIAL   LIFE. 


341 


conical  incisors,  long,  powerful  canines,  compressed  laterally,  and 
minutely  serrated  behind,  together  with   conical  molars   (Figs. 


FIG.  263.— Oudenodon  Bainil. 
(Owen.) 


FIG.  261.  — JAWS  OF 
Lycosaurus.  SIDE 
VIEW.  (Owen.)  c, 
c,  Canines. 


FIG.  262.— JAWS  or 
Cynodraco  serri- 
dens.  FRONT 
VIEW.  (Owen.) 


FIG.  ZM.—Dicynodon  lacertipes. 
(Owen.)  SHOWING  THE  MAX- 
ILLAKYTUSK.  TRIAS  OF 
SOUTH  AFRICA. 


261  and  262).     In  the  same  bed 

occur   representatives   of   another 

order,  AXOMODONTIA,  or  Dicyn- 

odontia,  "Dog-toothed,"  in  which  the  jaws  are  converted  into 

toothless  beaks  (Fig.  263).     In  some,  however,  there  was  a  pair 


FIG.  2&>.—Pterodactylu8  crassirostris.    FROM  LITHOGRAPHIC  SLATES  OF  SOLENHOFEN. 
(D'Orbigny.)    Erroneously  represented  with  five  anterior  digits  instead  of  four.     X  ?• 

of  teeth  implanted  in  the   upper  jaw,  growing  from  persistent 
pulps,  and  assuming  the  character  of 'great  tusks  (Fig.  264.) 


342 


GEOLOGICAL   STUDIES. 


The    air,    finally,   had    its   reptilian   denizens,   PTEROSAURIA, 
"  Flying  Saurians,"  having  essentially  the  structural  characters 


FIG.  2ffi.—Dimorphodon  macronyx.    (After  Owen.) 

of  a  reptile,  but   with  some  bird-like  modifications,  and  a  pair 
of  leathery  wings  stretched  from    the  greatly  elongated  outer 

digit,  along  the  side 
of  the  body  to  the 
tail.  We  find  five 
modifications  of  Fly- 
ing Saurians,  all 
European  but  one: 
(1)  Pterodactylus, 
having  the  jaws 
toothed  to  the  tip, 
and  tail  short,  Fig. 
265;  (2)  Dimorpho- 
don  (Fig.  266),  with 
jaws  toothed,  the 
anterior  teeth  larg- 

OG"t"          fl  Y\(\        fi^ll         VPT*V 

ViG.WZ.—Archceopteryxmacroura.    (After  Owen.)  St>     '  J 

long;      (3)     Rham- 

phorhynehus,  with  tips  of  jaws  edentulous,  and  tail  very  long; 
(4)  Pteranodon,  with  jaws  toothless  and  tail  short  and  slender  — 


PROGEESS   OF   TERRESTRIAL   LIFE. 


343 


comprising  gigantic  forms  from  the 
Cretaceous  of  North  America,  some 
having  a  spread  of  23  feet;  (5)  Or- 
nithopterus,  with  a  wing-finger  hav- 
ing only  two  phalanges. 

If  to  the  reptilian  forms  men- 
tioned we  add  the  other  Permian 
and  Mesozoic  forms  known  —  true 
Lizards,  Crocodilians,  Stegosaurians 
(plated  lizards),  and  other  genera 
of  savage  Theropods  (beast-footed), 
like  Megalosaurus,  and  Lcelaps,  and 
other  reptiles  with  hollow  bones,  the 
CCELUBIA  of  Marsh  —  we  may  easily 
believe  that  the  "Age  of  Reptiles" 
was  one  of  marvellous  luxuriance 
and  diversification  of  the  reptilian 
type. 

§9.     Toothed  Birds. 

While  the  Age  of  Reptiles  was 
in  progress,  true    Birds    came    into 
existence.     One  of  the  earliest  forms 
was  Archceop'  teryx  macron' ra  (Big- 
tailed  Old-flyer),  of  which  a  restora- 
tion by  Owen  is  given  in  Fig.  267. 
It  comes  from  the  Juras- 
sic schists  of  Solenhofen. 
It  had    a   conspicuously 
long,     vertebrated     tail, 
quill-bearing     on     each 
side;  and  Marsh  has  re- 
cently shown  that  it  pos- 

.  2 6 8. -LEFT  FIG.  269. -LEFT       "— "         sessed  teeth.      Whether 
LOWER  JAW  OF       LOWER  JAW  OF  FIG.  270,-Tooth  more  a  bird  than  reptile 
Ichthyornis  dis-       Hesperornis  reg-      OF  Hesperor-  , 
par.    X2.  ate.    xi  nis.    x  4.       is    even    still   a    mooted 


344  GEOLOGICAL   STUDIES. 

point.  Carl  Vogt  pronounces  it  a  feathered  lizard.  There  are 
two  conical  teeth  in  the  upper  jaw;  eight  neck  vertebrae,  with 
five  pairs  of  ribs  directed  backward;  ten  dorsal  vertebrae  without 


FIG.  271.— SKELETON  OF  Hesperornis  regalis,  RESTOBED.  (After  Marsh.)    X  iV- 

spinous  processes,  and  supporting  ribs  without  uncinate  pro- 
cesses; five  sternal  ribs,  and  very  minute  sternum.  The  fore 
limb,  he  maintains,  is  not  a  proper  wing,  and  there  are  three 


PROGRESS    OF   TERRESTRIAL   LIFE.  345 

digits,  resembling  those  of  a  clawed  lizard.  If  the  feathers  had 
not  been  preserved,  no  one  would  have  thought  the  Archceop- 
teryx  a  bird,  or  capable  of  flight.  Here,  then,  is  a  creature  in 
which  bird  and  reptile  are  so  mixed  that  the  best  judges  cannot 
agree  whether  it  is  one  or  the  other. 

Equally  remarkable  forms  have  been  described  by  Marsh, 
from  American  Cretaceous  strata,  on  which  he  has  founded  the 
Sub-Class  ODONTOBNITHES,  with  two  Orders,  Odontolcce,  having 
teeth  in  grooves,  and  Odontotormce,  having  teeth  in  sockets. 
The  tail  was  not  specially  elongated.  Some  of  their  charac- 
ters are  illustrated  in  Figs.  268-271. 

These  "  connecting  links "  between  reptiles  and  birds  pos- 
sess extreme  interest.  Whatever  conclusions  they  may  sustain 
respecting  the  genetic  relationship  between  these  two  types,  ex- 
ternally so  dissimilar,  the  nature  of  the  structural  relations  is 
identical  with  that  which  runs  through  all  the  numerous  and 
diversified  Orders  of  reptiles,  and  also  allies  reptiles  with  all  the 
other  vertebrate  classes. 

§  10.     Mammals. 

1.  Mesozoic  Mammals.  The  earliest  discovered  traces  of 
Mammals  occur  in  the  Upper  Triassic  strata  of  the  Old  World, 
and  in  strata  of  nearly  the  same  age  in  America.  They  are  single 
species  in  each  case.  The  next  remains  occur  in  the  Jurassic. 
The  Cretaceous  passes  with  the  disclosure  of  only  a  single  relic, 
found  in  America.  But,  with 
the  opening  of  the  Caenozoic 
^Eon,  mammalian  life  appears  to 
have  been  abundant. 

The  Triassic  Mammal  of  Eu-  FlG  m_ LOWER  JAW  or  Dromath&rium 
rope  has  been  named  Microlestes  sylvestrt,  EMMONS,  FROM  THE  JURA  TRI- 

T-^  AS  OF  NORTH  CAROLINA.     (After  Em- 

antiquus]  that ot  America,  JUrom-      mons) 

atherium  sylvestre,   E  m  m  o  n  s, 

from  the  red  sandstones  of  North  Carolina.  These  have  been 
generally  regarded  as  Triassic ;  but  Professor  Fontaine's  recent  de- 
termination of  the  Jurassic  age  of  the  Richmond  and  Deep  River 


346 


GEOLOGICAL   STUDIES. 


coal  fields  may  fix  a  later  epoch  for  Dromatherium.     The  Triassic 

mammal  of  South  Afri- 
ca is  Tritylodon  longce- 
vus  (Owen),  as  large 
as  a  gray  fox,  and  re- 
markably specialized 
for  a  mammal  so  an- 
cient. 

Judging  from  a  sin- 
gle ramus  of  the  lower 
jaw  of  Dromatlierium, 
Fig.  272,  the  animal  was 
an  insectivorous  Mar- 
supial, related  to  the 
Banded  Anteater  of 
Australia,  Myrmecobi- 
us  fasciatus,  Fig.  273. 
Microlestes  is  believed 
to  be  nearly  related. 
The  next  horizon  of  mammalian  remains  is,  in  the  Old  World, 

in  the  Stonesfield  Slate  of  the  Lower  O5lite.     According  to  com- 


FIG.  273. — Myrmecobius  fasciatus.    THE  BANDED  ANT- 
EATEK  or  NEW  SOUTH  WALES.    X  i-     (After  Gould). 


FIG.  214.—Amphitherium  (Thylacotheriuiri)  Broderipii.    X2.     FIG.  Zlb.—Phascolothe- 
rium  Bucklandi.     X  2. 

mon  opinion,  they  all  belonged  to  Marsupials.  Amphitherium 
(Fig.  274),  Amphilestes  and  Phase olot her ium  (Fig.  275)  were 
also,  probably,  Insectivores.  Stereognathus  appears  to  have  been 
herbivorous.  Toward  the  close  of  the  Oolitic  period,  the  Middle 


PROGRESS   OF   TERRESTRIAL   LIFE. 


347 


Purbeck  beds  supply  another  deposit  of  small  mammalian  re- 
mains, amounting1  to  14  species,  all  considered  marsupial  and 
polyprotodont  —  that  is,  having  more  than  two  lower  incisors, 
with  canines  more  or  less  extensively  developed,  and  the  molars 
either  cuspidate  or  with  sectorial  crowns.  Of  these,  Plagiau'lax 
is  allied  to  the  Kangaroo  rats,  having  large  premolars  with  seven 
conspicuous  grooves  on  the  crowns.  The  other  genera,  Spalaco- 
the'rium,  Tricon'  odon,  and  G-alastes  are  Insectivores,  and  related 
to  Australian  Phalangers.  Perathe' rium,  from  the  Paris  and 
American  Eocene,  was  an  opossum. 

The  Atlantosaurus  Beds  of  the  American  Jurassic  have 
yielded  not  less  than  17  species  of  mammals,  all  of  which  are 
probably  marsupial  or  re- 
lated to  marsupials,  and 
most  of  which  are  insect- 
ivorous, and  related  to 
European  forms.  Dryo- 
les'tes  prisons  was  a  small 
opossum.  Four  other  spe- 
cies of  Dryoles'tes  are 
known.  Sty  lac' odon,  2 
species,  was  a  near  relative  of  the  European  Stylodon.  Ctenac'  - 
odon,  2  species  (Fig.  276),  was  akin  to  Plagiau'lax,  and  the  two 
are  constituted  by  Marsh  the  types  of  a  new  order,  ALLOTHE'RIA, 
supposed  combining  marsupial  and  other  characters,  and  now 
extinct.  The  names  of  the  other  genera  are  Tin'  odon,  4  species, 
Dyplocyri  odon  (Fig. 
277),  Tricon' odon,  Al'lo- 
don,  and  Doc'  o don.  These 
Marsh  associates  in  an- 
other new  order,  PANTO- 
THE'RIA,  to  which  he 
thinks  most  of  the  Euro- 
pean Jurassic  Mammals  FiQ.Wl.— Dyplocyn'odon  victor,  Mil.  x  li-  a,  in- 
.rTr,-.^,  „  cisor;  6,  condyle;  c,  coronoid  process ;  d,  angle. 

belong.     With  lew  excep- 
tions, he  says,  the  Mesozoic  Mammals  are  low,  generalized  forms, 


FIG.  Zlti.—  Ctenac'odon  serratus,  MH.  X  2?-  LEFT 
LOWER  JA\V.  From  the  Jurassic  of  Wyoming 
Territory. 


348  GEOLOGICAL   STUDIES. 

without  any  distinctive  Marsupial  characters.  Not  a  few  of  them 
show  features  that  point  more  directly  tc  Insectivores.  From 
this  Order  true  Marsupials  and  Insectivores  were  probably  derived. 
From  the  Laramie,  or  highest  group  of  the  Cretaceous,  Cope 
described,  in  1884,  a  single  Mammal,  Meniscoes' sus  conquis'tus, 
discovered  by  J.  E.  Wortman  in  Dakota.  It  belongs  to  the 
Plagiau' lax  family. 

2.  Tertiary  Mammals.  By  such  beginnings  the  Mammalian 
Class  was  introduced  upon  the  earth.  During  two  entire  Meso- 
zoic  Ages  they  were  small  and  feeble  creatures,  either  low  Mar- 
supial in  type  or  else  even  lower  than  Marsupial,  and  marking 
Orders  from  which  the  Marsupial  characters  had  not  yet  been 
clearly  differentiated.  It  must  be  said,  however,  that  the  Marsu- 
pial, after  a  few  oviparous  Monotremes,  is  the  lowest  known  Mam- 
malian organization,  and  an  antecedent  improbability  exists  of 
any  older  order  generalizing  marsupial  and  placental  Mammals. 

With  the  opening  of  the  Tertiary  Age  a  rich  mammalian 
fauna  was  in  possession  of  the  continents  —  at  least  of  America 
and  Europe.  We  are  unable  to  say  whether  they  generally  pos- 
sessed marsupial  characters  or  not;  but  there  is  little  evidence 
that  they  did.  They  are,  however,  highly  generalized  forms. 
None  of  our  modern  Orders  had  become  distinctly  differentiated, 
but  several  of  them  were  pre-indicated  with  considerable  salience. 

There  were  characters  be- 
longing to  Insectivores,  Car- 
nivores,  Rodents,  Pachy- 
derms of  different  tribes, 
and  even  of  Proboscidians; 
but  they  were  variously  asso- 
ciated in  the  same  animals. 
One  of  the  earliest  of  these 
comprehensive  types  in 
America  and  Europe  was 
Coryph'odon,  Owen  (including  Batli 'modon,  Cope),  from  near 
the  bottom  of  the  Eocene.  An  outline  of  the  skull  is  shown 
in  Fig.  278,  in  which  the  small  size  of  the  brain  is  indicated. 


PROGRESS    OF   TERRESTRIAL    LIFE. 


349 


This  was  a  large  tapir-like  quadruped.  The  limbs  were  short, 
and  each  of  the  feet  was 
supplied  with  five  function- 
al digits  (Figs.  279,  280). 
Cope  describes  12  American 
species  of  Coryphodon  and 
two  of  Bathmodon.  ^ 

Of  nearly  the  same  age  E      in         IV  c 

as  the    Coryph'odon  was  a  FlG.  m_LEFT  FoRE  FoOT.   xi 
strange  animal  which  Marsh    FIG.  280. -LEFT  HIND  FOOT.    XT- 
has     named      Tillothe' rium 

fo'diens,  and  made  the  type  of  a  new  Order,  TILLODONT'IA. 
It  presents  a  remarkable  combination  of  the  characters  of 
Ungidata,  Rodentia, 
and  Carnivora.  The 
skull  (Fig.  281)  resem- 
bles that  of  a  bear,  and 
the  skeleton  generally 
is  that  of  Carnivores; 
but  the  feet  are  5-toed 
and  plantigrade.  The 
premolars  and  molars 
have  grinding  crowns,  FIG.  281 
the  canines  are  of  small 
size,  and  the  premaxil- 
laries  carried  a  pair  of  scalpriform  incisors,  like  the  beaver's  in 
form  and  in  growing  from  persistent  pulps.  Anchippodus,  Leidy 
( —  Trogosus),  was  allied  to  Tillotherium. 

Another  interesting  form,  from  the  Wahsatch  Eocene  of 
Wyoming,  is  Phenac  odus,  Cope,  a  skeleton  of  which,  in  the 
position  in  which  it  was  found  imbedded  in  the  sand-rock,  is 
shown  in  Fig.  282.  Its  nasal  bones  and  several  other  features 
resemble  the  tapir;  the  tail  was  as  long,  proportionally,  as  that 
of  a  cat;  the  hind  feet  were  semi-plantigrade;  the  molar  teeth 
were  pig-like.  Of  Plienacodus  Cope  has  described  thirteen  spe- 
cies, and  has  made  it  the  type  of  a  family  and  of  a  Sub-order 


TiUothe'rium  fo'diens,  MH.  WITH  THE 
LOWER  JAW  DISPLACED  DOWNWARD.  X  iV 
(After  Marsh.) 


350 


GEOLOGICAL   STUDIES. 


CO^DYLAR'THRA,  which,  with  Hyracoidea,  the  Conies,  he  unites 
in  the  new  Order,  TAXEOPODA. 


PIG.  282.—Phenac'odus  Wortmani,  COPE,     x  iV    WAHSATCH  GROUP,  WYOMING.    (After 
Cope.) 

Another  Wahsatch  form,  found  also  in  Wyoming,  is  named 
Mes' onyx  by  Cope.     The  lower  jaw  is  here  figured.     (Fig.  283, 

a,  b.)  This  animal  was 
distinctly  flesh-eating, 
but  in  some  respects  it 
differed  from  modern 
Carniv'ora,  and  Cope 
has  established  a  new 
Order,  CREODON'TA,  to 
receive  this  and  numer- 
ous other  extinct  flesh 
eaters, which  he  arranges 
in  eight  families.  They 
were  also  related  to  Mar- 
supials and  Insectivores. 
One  group  of  them  (the 
Tillodontia  of  Marsh) 

was    rodent,  with    lemurine  tendencies,  and   the   other,    Tcenio- 
donta,  was  edentate. 


FIG.  283.—  Mesonyx  ossif'ragus,  COPE.  WAH- 
SATCH OP  BIG  HORN  RIVER,  WYOMING.  (After 
Cope.)  x  T-  «i  side  view  of  mandible;  &,  view 
from  above. 


PROGRESS    OF   TERRESTRIAL   LIFE. 


351 


In  the  next  or  Bridger  epoch  of  the  Eocene  existed  in  Wyo- 
ming an  assemblage  of  quadrupeds  elephantine  in  dimensions 
and  striking  in  organization.  These  have  been  made  the  subject 
of  an  elaborate  memoir  by  Marsh,  in  which  an  extinct  sub-order 
has  received  an  elucidation  unequalled  in  the  history  of  science. 
They  have  also  been  very  thoroughly  investigated  by  Cope  and 
Leidy,  and  have  been  embraced  within  the  researches  of  Osborne 
and  Spier.  The  DINOCER'ATA  of  Marsh  are  constituted  of  three 
genera:  Uintatherium  (=  Hathyop'sis,  Cope),  Dinoc' eras,  and 
Tinoc1 'eras  (=  Eobas' ileus,  Cope).  With  the  DINOCER'ATA 
Marsh  unites  the  CORYPHODON'TA  (=  PANTODON'TA,  Cope)  to 
constitute  the  Order  AMBLYDAC'TYLA,  which  appears  to  be  pre- 
cisely identical  with  Cope's  older  named  AMBLYP'ODA.  This, 
with  the  orders  PROBOSCID'EA,  HYRACOID'EA,  and  CLINODAC'- 
TYLA  (=  Perissodactyla  -{-  Artiodactyla)  form  Marsh's  Super- 
Order  UNGULATA.  It  would  be 
out  of  place  here  to  enumerate 
the  characters  of  these  genera. 
The  student  will  get  an  impres- 
sion of  the  aspects  of  these 
primitive  beasts  from  the  skulls 
and  skeletons  here  figured.  It 
is  obvious  that  the  feet  resem- 
ble, except  in  technical  points, 
those  of  Coryph1 '  odon,  and  also 
those  of  the  elephant.  A  cast 


FIG.  284.—  Uintathe'rium  Leidya'num, 
SKULL.  X  ^  BRIDGER  GROUP,  WTO- 
MING.  (After  Osborne.) 


FIG.  285.— FEET  OF  Dinoceras  mirabile,  MARSH.    ( Uintatherium  mirabile  of  Cope, 
Leidy,  and  Osborne.)    x  |.  a,  Fore  Foot;  6,  Hind  Foot.    (After  Marsh.) 


352  GEOLOGICAL   STUDIES. 

of  the  brain  shows  the  very  small  size  of  the  hemispheres  and  the 
very  large  olfactory  lobes.  The  brain  is  the  most  reptilian  among 
mammals.  In  Fig.  286  is  a  restoration  of  the  skeleton  of  Dinoc' '- 


FIG.  'ZM.—Dmoc'eras  mirab'ile,  MH.    x  IT-    BRIDGEK  GROUP,  WYOMING.    (After  Marsh.) 

eras.  In  Fig.  287  is  a  similar  restoration  of  Tinoc' eras  or 
Eobas' ileus.  The  student  will  notice  in  all  these  a  similar  struc- 
ture of  the  feet,  and  similar  protuberances  on  the  skull.  It  is 
uncertain  whether  these  were  surmounted  by  horns  or  only  cov- 


FIG.  Wn.—Tmoc'eras  ingens,  MH.  x  .fa.     BRIDGER  GROUP,  WYOMING.     (After  Marsh. 


ered  by  thick  skin.  In  either  case,  they  served,  probably,  as 
weapons  of  attack.  The  enormous  canines  served  a  similar  pur- 
pose. 

The  Dinocerata,  according  to  Cope,  are  composed  of   Eobas- 
ileus  (  =  Tinoceras,  Marsh),  Loxolophodon  (included  in  Tinoc- 


PKOGEESS   OF   TERRESTRIAL   LIFE. 


353 


eras  by  Marsh),  Bathyopsis  (  =   Uintatherium,  pars,  of  Marsh), 
and  Uintatherium,  Leidy. 

Passing  unmentioned  a  multitude  of  remarkable  Eocene 
forms,  we  reach  the  White  River  Beds  of  the  Miocene,  and  find 
in  existence  another  type  of  elephantine  quadrupeds.  The 
Brontothe'rium,  Marsh  (—  Sym bor'  odon,  Cope,  +  Miobas' ileus, 
Cope),  of  which  a  skull  is  shown  in  Fig.  288,  had  four  nearly 


FIG.  288.—Brontothe'rium  ingens,  MH.    WHITE  RIVER  BEDS  OF  THE  MIOCENE. 
(After  Marsh.)    x  t^- 

equal  toes  on  the  fore  foot  and  three  on  the  hind  foot,  thus 
numerically  resembling  the  tapirs.  In  size  and  general  conform- 
ation of  the  skeleton  it  resembled 
the  elephant,  but  with  shorter  limbs. 
The  nose  was  probably  long  and 
flexible,  but  without  a  proboscis. 
The  brain  cavity  was  very  small. 
A  pair  of  horncores  rose  on  the  max- 
illary bones.  The  canines  were  short, 
and  separated  by  a  diastema,  or  in- 
terval, from  the  premolars.  The 
student  may  point  out  from  the 
illustrations  the  differences  among 
the  great  extinct  mammals. 

The  Tertiary  ages  of  other  conti- 
nents   were    equally    productive    of 
mammalian   forms;    but    we   can  only  afford  space   for  mention 
of  two.     The  Dinothe'rium  was  about  the  first  known  of  Pro- 


FIG.  289.—  Dinothe'rium  gigan- 
teum,  KAUP.  CONTINENT  OF 
EUROPE.  (After  Kaup.) 


354  GEOLOGICAL   STUDIES. 

boscidians.  Its  remains  have  been  found  in  Germany,  France, 
and  Greece,  in  deposits  of  Miocene  age.  It  had  in  the  lower  jaw 
two  enormous  tusk-like  incisors,  directed  vertically  downward. 
The  molars  present  a  combination  of  mastodont  and  tapiroid 
characters.  The  animal  attained  enormous  size,  and  by  some 
it  is  thought  to  have  been  of  semi-aquatic  habits.  The  other  for- 
eign mammal  to  be  mentioned  is  the  Sivathe'  rium  of  the  Sivalik 
Hills  in  India,  a  gigantic  four-horned  Antelope.  The  posterior 
horns  possessed  two  snags  or  branches,  a  peculiarity  not  to  be 
paralleled  among  existing  Cavicor'nia,  except  in  the  Prong- 
buck.  Bramathe' rium  was  a  contemporary  of  similar  organi- 
zation. 

We  must  mention,  lastly,  the  succession  of  horse-like  forms 
that  have  existed  in  America  during  the  progress  of  the  Tertiary 
ages..  These  have  been  worked  out  by  Marsh,  to  whom  science  is 
indebted  for  so  many  important  results.  Much,  however,  has 
been  contributed  by  Cope  and  Leidy,  and  it  is  not  certain  that 
some  of  their  names  are  not  possessed  of  priority  over  Marsh's. 

Animals  somewhat  horse-like  were  in  existence  at  the  begin- 
ning of  the  Eocene.  Other  species  appeared  in  succession,  pro- 
gressively more  and  more  like  the  modern  horse,  until,  near  the 
close  of  the  Tertiary,  the  modern  genus  Equus  appeared.  It 
would  not  be  proper  to  enter  here  into  the  details  which  charac- 
terize and  differentiate  these  successive  equine  forms;  but  the 
student  may  refer  to  the  illustrations,  Fig.  290,  while  he  reads 
the  following  brief  statements: 

In  the  oldest  Eocene  deposits  of  New  Mexico  are  found  the 
remains  of  a  horse-like  quadruped,  Eoliippus  (=  Hyracothe' - 
rium?),  about  the  size  of  a  fox.  It  had  four  functional  toes 
before  and  three  behind,  thus  resembling  the  tapir.  A  rudiment 
(like  a  "splint  bone")  remained  of  the  outer  or  Vth  toe  behind 
(since  those  present  were  the  lid,  Hid,  and  IVth);  and  since  the 
Vth  was  present  before,  there  was  probably  a  rudiment  of  the  1st 
in  the  fore  foot,  making  the  normal  number  of  five  digits  in  that 
foot.  The  "hoofs"  were  mere  thick,  broad,  and  blunt  claws. 
The  molars  were  short  and  without  "  cement."  There  were 


RE.CENJ 


JEquus 


PROGRESS   OF   TERRESTRIAL   LIFE. 

1.  2.  3.          4.  5.  6. 


355 


PLIOCENE 


Pliohippus 


Protohippus 


Mesohippus 


EOCENE 


Orohippus  Or 
Hyracotherium 


FIG.  2SO. — SUCCESSION  OF  EQUINE  TYPES.    (Marsh.)    See  Explanation,  page  354. 


356  GEOLOGICAL   STUDIES. 

eight  carpal  bones,  resembling  those  of  the  tapir.  This  genus 
is  not  illustrated  in  Fig.  290. 

In  the  Middle  Eocene  or  Bridger  Beds,  of  Wyoming  and 
Utah,  existed  Orohippus,  also  of  the  size  of  a  fox.  This  had 
four  functional  toes  before  and  three  behind.  The  ulna  was  com- 
plete and  distinct  from  the  radius.  The  tibia  and  fibula  were  also 
distinct.  The  crowns  of  the  molars  were  exceedingly  short,  and 
the  enamel  pattern  simple.  Later  in  the  Eocene  lived  Epihippus 
which  resembled  Orohippus  in  the  digits,  but  differed  in  its 
more  developed  molars. 

In  the  early  Miocene  lived  Mesohippus,  a  horse-like  quadru- 
ped of  the  size  of  a  sheep.  Its  functional  toes  had  diminished  to 
three  before,  nearly  equal,  and  three  behind.  In  the  fore  limb, 
however,  was  a  large  u  splint,"  the  remnant  of  the  Vth  digit  of 
Orohippus.  The  radius  and  ulna  were  still  distinct,  but  the 
latter  was  considerably  attenuated  in  the  lower  part.  The  tibia 
and  fibula  were  also  distinct. 

In  the  late  Miocene  of  Oregon  existed  Miohippus,  also  of  the 
size  of  the  sheep,  with  three  functional  toes  before  and  three  be- 
hind, and  also  a  splint  of  the  Vth  digit  before,  but  smaller  than  in 
Mesohippus.  The  middle  hoof  is  also  larger  and  the  lateral  hoofs 
are  shrunken.  The  ulna  is  still  distinct  and  as  long  as  the  radius, 
but  very  slender  distally.  The  fibula  is  coossified  with  the  tibia 
at  the  lower  end.  The  older  Miocene  Anchitherium,  the  oldest 
equine  known  in  Europe,  is  closely  related,  but  a  little  more 
specialized. 

Coming  down  to  the  early  Pliocene,  we  find  that  a  horse-like 
quadruped  existed,  called  Protohippus,  of  the  size  of  an  Ass. 
Instead  of  three  serviceable  toes  it  had  but  one  with  a  dangling 
hooflet  or  "  dew-claw  "  on  each  side.  The  ulna  was  as  long  as 
the  fore  arm,  but  extremely  slender.  The  fibula  was  rudimen- 
tary. The  crowns  of  the  molars  were  still  longer  than  in  Mio- 
hippus.  Contemporary  with  this,  were  the  closely  related  An- 
chippus  in  America  and  Hipparion  (  =  Hippothe' riuni]  in 
Europe;  while  Merych'ius  was  probably  identical. 

Next,  in  the  Middle  Pliocene,  existed  Pliohippus,  of  the  pro- 


PROGRESS   OF   TERRESTRIAL   LIFE.  357 

portions  of  a  moderate-sized  horse,  in  which  was  only  a  median 
toe,  larger  than  in  Protohippus,  but  with  large  splints  instead  of 
dangling  hooflets,  on  each  side.  The  crowns  of  the  upper  molars 
were  longer  and  the  crescentic  areas  more  complicated  than  in  the 
older  types. 

Finally,  toward  the  end  of  the  Pliocene,  Equus,  the  modern 
horse,  existed  in  America.  It  differred  from  Protohippus  in  a 
more  powerful  middle  digit,  diminished  splint  bones,  upper 
molar  crowns  larger  and  more  elongated,  and  crescentic  areas, 
formed  by  the  enamel  plates,  more  complicated.  The  horse  sub- 
sequently found  its  way  to  the  Old  World  and  remained  to  his- 
toric times.  Meantime  it  became  extinct  in  America,  and  was 
reintroduced  on  the  discovery  of  the  New  World  by  civilized 
man. 

The  historical  vicissitudes  of  the  Camel  have  been  similar. 
These  and  many  other  facts  indicate  that  the  Old  World  received 
some  of  its  Mammalian  populations  from  the  New. 

§11.     Retrospect  of  Succession  of  Vertebrate  Life  in  America. 

The  following  Table,  compiled  from  final  publications  of 
Marsh  and  Cope,  exhibits  the  order  of  introduction  of  the  princi- 
pal vertebrate  types  in  America,  with  a  corresponding  grouping 
of  formations.  The  student  of  geology  will  find  it  useful  for 
reference. 


358 


GEOLOGICAL   STUDIES. 


•oiozoanva 


12.     Conspectus  of  the  Geological  Range  and  Relative  Expan- 
sion of  the  Principal  Types  of  Animal  Life. 


Dinosauria 
Aves 

Mammalia 
••• 
FIG.  291.— TABLE  OF  RANGE  AND  EXPANSION  OF  ORGANIC  TYPES. 


CHAPTER  V. 
FORMATIONAL  GEOLOGY. 

FORMATIONS,  THEIR   STRATIGRAPHICAL  CONSTITUTION,  GEOGRAPH- 
ICAL   EXTENSION,  AND    PALJEONTOGRAPHICAL 
CHARACTERISTICS. 

§1.     Preliminaries.     Geological  Maps. 

WE  must  now  return  to  the  rocks,  and  learn  more  method- 
ically what  are  the  lithological  characters  of  the  various  groups 
into  which  they  are  arranged,  as  heretofore  shown  (page  274), 
their  thickness  and  relative  importance,  the  fossil  remains  which 
characterize  them,  and  the  regions  in  which  they  occupy  the 
earth's  surface. 

By  the  aid  of  the  classification  which  has  been  already  studied 
to  a  considerable  extent,  and  the  geological  map  of  the  Eastern 
United  States,  on  which  numerous  exercises  have  been  had,  with 
the  general  survey  of  organic  life  contained  in  the  last  chapter,  a 
good  preliminary  acquaintance  has  been  made  with  the  forma- 
tions which  we  are  now  to  study  a  little  more  in  detail,  or  at  least 
in  a  somewhat  different  manner. 

To  prepare  the  way  for  a  broader  and  completer  comprehen- 
sion of  American  geology,  we  now  direct  the  particular  attention 
of  the  student  to  both  parts  of  the  Geological  Map  of  the  United 
States  on  pages  118  and  119. 

To  enable  the  student  to  acquire  a  grasp  of  the  method  of 
continental  development,  we  also  introduce  here  a  very  general 
map  of  the  geology  of  North  America  : 


FORMATIONAL   GEOLOGY. 


361 


PALEOZOIC  MESOZOIO 

FIG.  292.— GEOLOGICAL  MAP  OF  NORTH  AMERICA. 


QUATERNARY. 


§  2.     The  Eozoic  Great  System. 

1.  How  the  Term  is  Used.  A  glance  at  the  geological  maps 
shows  that  the  rocks  of  this  Great  System  occupy  but  compara- 
tively little  of  the  actual  surface  of  North  America.  But  when 
we  reflect  that  they  pass  everywhere  under  the  other  rocks,  we 
understand  that  they  constitute  the  great  mass  of  the  solid  land. 
Because  they  constitute  the  beginning  of  the  actually  observed 
series  of  formations,  some  geologists  designate  them  Archcean, 
from  ap%ri,  the  beginning.  But  we  know  too  little  about  the  deep- 
est and  oldest  rocks  to  assert  that  formations  seen  at  the  surface 
continue  down  and  include  the  rocks  formed  in  the  beginning. 
We  have  good  reason  to  believe,  as  before  explained  (page  288), 
that  the  beginning  rocks  have  been  long  ago  melted  away.  We 
do  not  know  that  any  archaean  rocks  remain.  Assuredly,  we  have 
not  seen  any  archaean  rocks;  and  it  is  certain  they  are  not  strati- 


362  GEOLOGICAL   STUDIES. 

fied,  as  the  oldest  rocks  known  to  observation  are.  We  may  reason 
about  archasan  rocks,  as  a  necessity  of  our  theory  of  the  world.  We 
may  even  extend  the  meaning  of  the  term  to  embrace  all  the  rocks 
from  the  beginning  of  incrustation  to  the  Cambrian.  We  may  some- 
times use  the  term  in  this  sense.  But  we  need  a  term  to  desig- 
nate these  later  archsean  rocks,  and  hence  we  style  them  Eozoic — 
a  term  symmetrical  with  Palaeozoic,  Mesozoic,  and  Csenozoic,  and 
one  which,  unlike  Azoic  (formerly  employed),  can  never  become 
inapplicable  through  the  progress  of  discovery.  The  rocks  next 
before  the  Eozoic  were  perhaps  strata  now  melted  away.  Before 
all  strata  there  must  have  existed  a  fire-formed  crust  —  a  real 
Pyrogenic  formation.  Hence,  Archaean,  in  the  sense  suggested, 
is  comprehensive,  and  we  need  to  note  its  divisions. 
2.  Divisions  of  the  Great  System. 

(  Keweenian  System. 

Eozoic  Great  System,  -j  Huronian  System. 
[  Laurentian  System. 

The  name  Azoic  was  applied  to  rocks  older  than  the  lowest 
known  fossiliferous  strata  by  Messrs.  Foster  and  Whitney  in  their 
Government  report  on  the  Mineral  Region  of  Lake  Superior.  By 
Sir  William  Logan  and  his  associates  rocks  holding  this  position 
in  Canada  were  divided  into  Laurentian  and  Huronian,  from  the 
Laurentide  Hills  and  Lake  Huron.  Very  much  discussion  has 
been  subsequently  had,  and  is  still  in  progress,  respecting  the 
classification  of  these  pre-Cambrian  rocks;  and  this  has  acquired 
new  interest  in  connection  with  the  public  surveys  still  in  prog- 
ress in  Minnesota,  Wisconsin,  and  Michigan.  Western  studies 
seem  to  have  established  the  existence  of  a  Copper  Bearing  (Ke- 
weenawan  or  Keweenian)  Series  above  the  proper  Huronian  and 
older  (as  is  now  thought)  than  the  Cambrian.  This  System  we 
accordingly  introduce  here,  for  the  first  time,  we  think,  in  any 
text-book. 

At  the  same  time,  this  arrangement  must  be  regarded  as 
provisional.  It  will  be  shown  in  the  next  Section  that  an 
"Acadian"  or  "St.  John"  formation  is  known  on  the  eastern 


FORMATIONAL   GEOLOGY.  363 

border  of  the  continent,  and  also  in  Central  Nevada,  holding  a 
position  beneath  the  Potsdam  formation.  This  Acadian  is  not 
identified  in  the  Upper  Mississippi  region  ;  and  it  may  yet  be 
shown  that  the  Keweenian  is  its  chronological  equivalent.  Again, 
it  has  very  recently  (September,  1885)  been  shown,  by  N.  H. 
Winchell,  that  Cambrian  fossils  occur  in  the  "  Pipestone  "  of  the 
Upper  Missouri  River.  As  the  pipestone  is  embraced  in  the 
great  Quartzite  formation  underlying  the  Potsdam  in  Minnesota 
and  Wisconsin,  the  evidence  is  that  this  Quartzite  is  Cambrian, 
as  the  present  writer  long  ago  suggested,  instead  of  Huronian, 
as  maintained  by  the  Wisconsin  geologists.  If  so,  it  is  in  the 
position  of  the  St.  John  Slates  of  the  East,  and  may  be  their 
western  equivalent.  Like  the  Keweenian,  it  succeeds  downward 
the  Potsdam  Sandstone;  and  the  question  remains  open,  What 
are  the  relations  between  the  Copper  Bearing  Series  and  the 
Baraboo  Quartzite? 

3.  Geographical  Distribution  of  Surface  Exposures.  Eozoic 
rocks  at  present  occupy  the  surface  (1)  in  regions  where  no  later 
sediments  were  ever  deposited  over  them  in  consequence  of  the 
uplift  of  those  regions  above  the  sea  level;  (2)  in  regions  once 
overlaid  by  later  sediments  which  have  been  carried  away  by 
erosions;  (3)  in  places  where  they  have  been  thrust  up  through 
breaches  in  the  overlying  strata. 

Glancing  over  the  Geological  Map,  we  notice  one  principal 
belt  stretching  from  the  coast  of  Labrador  to  the  region  north  of 
the  Great  Lakes,  and  thence  northwest  to  the  Arctic  Ocean, 
covering  an  area  enclosing  Hudson's  Bay  like  an  arc  of  a  great 
circular  belt.  It  will  be  noticed  that  the  Adirondac  area  is  an 
appurtenance  to  this,  and  that  an  arm  stretches  southwestward 
into  Minnesota.  The  considerable  area  in  Michigan  and  Wiscon- 
sin may  be  regarded  as  simply  an  outlying  patch  of  the  same. 
This  is  the  great  Eozoic  nucleus  of  the  continent  —  at  least  of  its 
eastern  and  northern  parts.  It  is  the  Great  Northern  Eozoic 
Belt.  We  find  also  an  Appalachian  belt  stretching  from  Dutchess 
county,  New  York,  and,  with  some  interruptions,  from  New 
Brunswick  to  Georgia.  This  is  the  Great  Seaboard  Eozoic  Belt. 


364  GEOLOGICAL   STUDIES. 

Over  the  Rocky  Mountain  region,  and  westward  at  intervals  as 
far  as  the  Sierra  Nevada,  occur  isolated  areas  and  outcropping 
mountain  masses  and  ranges  of  Eozoic  rocks  which  have  been 
largely  concealed  by  later  sedimentation.  This  is  the  Great 
Cordilleran  Eozoic  Area.  Other  detached  island-like  areas  exist 
in  Missouri,  Texas,  and  other  regions. 

4  General  Constitution  of  the  Great  System.  The  Eozoic 
rocks,  as  far  as  accessible  to  us,  attain  an  enormous  thickness. 
We  have  studied  probably  95,000  feet  of  them  —  not  all,  of 
course,  in  one  connected  series.  We  find  them  to  be  almost 
wholly  crystalline  and  hard.  The  greater  part  are  phanerocrys- 
talline.  Nearly  all  known  minerals  are  embraced  in  them ;  the 
majority  are  even  restricted  to  them.  Here  are  found  in  place 
those  metamorphic  rocks  whose  kinds  we  have  already  studied  in 
the  bowlder  fragments  scattered  over  the  Northern  States.  Here 
are  the  great  masses  of  granites,  gneisses,  diorites,  and  diabases, 
whose  stratification  has  become  nearly  or  quite  obliterated. 
Here  are  most  of  the  different  species  of  schists.  Here  are  the 
marbles  and  serpentines.  In  these  old  crystalline  rocks  are 
enclosed  the  great  deposits  of  iron  ore  —  magnetite,  haematite, 
titaniferous  iron,  and  Franklinite,  or  zinc-iron  ore.  Here  are  our 
stores  of  graphite  and  soapstone  (steatite  and  parophite). 

These  rocks  show  almost  everywhere  evidences  of  great  dis- 
turbance. They  have  sometimes  been  tilted  up  at  steep  angles. 
Sometimes  they  are  quite  vertical.  Very  commonly  later  strata 
rest  on  the  exposed  and  worn  edges  of  the  Eozoic.  In  Fig.  38 
we  have  an  illustration.  On  the  left  are  gneisses,  #,  dipping  to 
the  left,  and  resting  against  the  central  mass  of  granite,  a.  On 
the  right  are  gneisses,  b,  dipping  toward  the  right  at  a  steep 
angle,  and  resting  against  the  other  slope  of  the  granite  nucleus. 
On  the  upper  edges  of  these  thick-bedded  gneisses  rest  uncon- 
formably  the  strata  of  sandstone,  c.  The  latter  are  not  Eozoic. 
The  gneisses  were  tilted  before  the  sandstones  were  laid  down. 
A  geological  convulsion  here  separates  two  ages  and  two  forma- 
tions. In  Fig.  107  the  horizontal  sandstones,  S,  are  seen  abutting 
against  the  slope  of  the  older  rocks,  Cy  and  the  underlying  and 


FORMATIONAL   GEOLOGY.  365 

still  older  beds,  If,  rest  against  broken  edges  of  the  formation,  L. 
The  relation  of  the  Eozoic  to  the  later  formations  is  well  shown, 
also,  in  Figs.  46  and  84. 

The  plication  of  the  Eozoic  strata  is  something  as  remarkable 
as  their  tilting.  The  section  of  the  Wisconsin  rocks,  Fig.  293, 
shows  their  condition  and  their  relation  to  the  higher  rocks.  In 
Mt.  Kearsarge,  Fig.  89,  we  find  another  instructive  example  of 
plications.  In  Fig.  294  we  reproduce,  from  Sir  William  Logan, 
a  section  through  the  Eozoic  strata  of  western  Canada.  Here 
the  crumpled  condition  of  the  strata  is  strikingly  shown.  The 
dotted  lines  are  intended  to  indicate  the  probable  connections 
of  the  formations. 

Lauren  tian  !        Huronian       j  Cambria  n 

2 

3 


FIG.  293.— GENERALIZED  SECTION  ACKOSS  THE  ROCKS  or  WISCONSIN.    (Chamberlin.) 
1.    Potsdam  Sandstone.    2.   Lower  Magnesian  Limestone.    3.    St  Peter's  Sandstone.    4. 
Trenton  Limestone.    5.  Galena  Limestone.    6.  Cincinnati  Shales.    7.  Niagara  Lime- 
stone.   8.  Lower  Helderberg  Limestone.    9.  Hamilton  Limestone. 

5.  Kinds  of  Rocks  and  Economic  Products.  The  Lauren- 
tian  System  contains  great  beds  of  granite,  syenite,  and  gneiss, 
with  some  mica-  and  much  hornblende-schist.  Hornblende  and 
pyroxene  are  very  abundant  minerals,  and  with  them  labradorite 
is  one  of  the  commonest  feldspars.  Iron  is  very  generally  dis- 
seminated, both  as  a  chemical  constituent  and  also  as  a  min- 
eral in  the  forms  of  magnetite,  hasmatite,  and  titaniferous  iron. 
There  are  also,  in  Canada,  three  great  beds  of  crystalline  lime- 
stone (Fig.  294),  with  many  intercalated  layers  of  gneiss  and 
rocks  consisting  largely  of  pyroxene  or  hornblende.  The  Lauren- 
tian  rocks  were  estimated  by  Logan  at  30,000  feet. 

The  Huronian  System,  as  commonly  understood,  is  composed 
of  beds  of  granular  and  conglomeritic  quartzites,  quartz-schists, 
jasper  and  chert  schists,  and  several  thick  formations  of  diorite 
and  diabase  which  sometimes  pass  into  granites  and  syenites; 
with  also  a  great  thickness,  higher  in  the  series,  of  hydro- mica 


366 


GEOLOGICAL   STUDIES. 


and   magnesian  schists,  and  black  slate  and  ferruginous  schists, 

terminated  by  enormous  beds  of  mica 
schist,  gneiss,  and  granite.  The  con- 
glomerates  contain  rounded  frag- 
ments  up  to  a  foot  in  diameter,  and 
with  the  quartzites,  attain  a  thick- 
ness of  2,500  feet.  The  great  iron 
deposits  of  northern  Michigan  and 
Wisconsin  are  associated  with  quart- 
zose  and  dioritic  rocks,  and  are  com- 
monly  regarded  Huronian. 

The  Keweenian  System  consists 
of  interstratified  igneous  and  sedi- 
mentary  beds.  The  former  are  mainly 
diabases,  with  some  norites,*  mela- 
phyrs,  and  porphyries;  the  latter  are 
conglomerates,  sandstones,  and  shales 
derived  mainly  from  the  igneous 
rocks.  The  conglomerates  are  formed 
of  the  debris  of  felsitic  and  quartz 
porphyries,  with  some  from  diabases. 
Some  of  the  conglomerate  fragments 
are  one  or  two  feet  in  diameter.  A 
single  bed  of  coarse  conglomerate  on 
the  Montreal  River  is  1,200  feet  thick. 
The  beds  are  tilted,  but  not  con- 


*  These  by  the  Wisconsin  and  Minnesota  geol- 
ogists, following  late  German  authorities,  are 
termed  "gabbros"—  a  name  which  ought  to  be 
allowed  to  rest  in  disuse.  (See  pages  53  and  77,  this 
work.)  Gabbro  is  denned  in  the  Wisconsin  Report 
as  follows:  "A  rock  formed  of  a  plagioclase  feld- 
spar and  diallage.  The  feldspar  is  usually  labra- 
dorite.  The  diallage  is  little  more  than  a  foliated 
augite.  Usually  more  coarsely  crystalline  than 
diabase.  The  Duluth  granite  is  a  typical  exam- 
ple.11 Norlte  with  them  is  composed  of  a  plagio- 
clase with  hypersthene  or  enstatite  (similar  to  hy- 
persthene,  but  light-colored).  See  page  77. 


FORMATIONAL    GEOLOGY.  367 

torted,  and  metamorphic.  Maximum  thickness  about  45,000  feet, 
of  which  over  15,000  feet  are  sedimentary.  Irving  separates 
them  into  an  Upper  division  wholly  sedimentary  —  mostly  red 
sandstone  and  shale  —  with  a  mean  thickness  of  15,000  feet,  and 
a  Lower  division  made  up  chiefly  of  basic  igneous  rocks  in  many 
sheets,  with  a  thickness  of  25,000  to  30,000  feet. 

Geologists  are  not  united  as  to  the  geological  position  of  the 
great  iron-ore  beds.  Those  of  northern  New  York  (See  Figs. 
103  and  104)  and  Missouri  are  commonly  represented  as  Lauren- 
tian,  and  the  similar  beds  in  North  Carolina,  Canada,  Sweden, 
and  Norway  are  believed  to  be  of  the  same  age.  But  the  Pilot 
Knob  and  Iron  Mountain  deposits  are  not  far  remote  stratigraph- 
ically  from  the  Lower  Magnesian  (Cambrian)  limestone.  The 
section  through  the  Penokie  Iron  Range,  too,  Fig.  107,  shows 
the  iron-bearing  beds  included  conformably  in  the  Huronian,  Jfy 
while  these  strata,  rest  quite  unconformably  against  the  edges  of 
the  Laurentian  strata,  L.  Not  unlikely,  the  rocks  inclosing  the 
iron  ores  of  northern  New  York  will  be  found  to  be  Huronian. 

The  mode  of  occurrence  of  iron  ores  and  other  particulars  will 
be  found  elsewhere  (pages  182,  69). 

The  great  copper  deposits  of  the  Lake  Superior  region  occur 
in  the  Keweenian  series.  They  exist  partly  in  the  igneous  rocks 
and  partly  in  the  sedimentary.  In  the  latter,  they  appear  to  be 
mostly  a  secondary  product,  introduced  after  the  sediment  was 
laid  down.  In  some  cases  the  metal  appears  as  an  original  con- 
stituent of  the  conglomerate.  In  the  Calumet  and  Hecla  mine, 
the  most  productive  in  the  world,  the  so  called  vein  is  simply  a 
conglomerate  8  to  12  feet  thick,  lying  between  massive  sheets  of 
trap.  The  native  copper  permeates  the  whole  mass,  and  serves 
as  a  cementing  material.  In  the  trap  rocks  the  copper  is  found 
filling,  either  alone  or  with  other  minerals,  the  amygdaloidal  cav- 
ities which  abound  near  the  lower  and  upper  surfaces  of  the 
sheets,  and  insinuating  itself  into  the  other  cavities  and  fissures. 
Sometimes  the  filled  fissures  assume  the  characters  of  true  veins. 

From  rocks  of  Laurentian  age  comes  most  of  the  graphite  of 
the  world.  (See  Part  I,  Study  XIII.)  They  afford,  also,  apatite, 


368 


GEOLOGICAL    STUDIES. 


a  phosphate  of  lime  used  in  agriculture;  rensselasrite  or  steatite, 
used  for  potstone  or  soapstone,  and  cut  into  slabs  for  chimney 

pieces,  furnace  linings, 
and  foot  warmers,  and 
used  also  for  ink- 
stands; parophite,  an 
aluminous  rock  used 
for  inkstands;  beds  of 
marble.  Formations 
perhaps  later  in  the 


FIG.  295. — PaloROphycus  arthrophycus,  WIN.  FROM  THE 
KEWEENIAN  SANDSTONE,  NORTH  FLANK  or  THE  POR- 
CUPINE MOUNTAINS.  (From  Nature.) 


series 


contain    slates 
and  deposits  of  lead  and  zinc  ores. 

6.  Organic  JRemains.  The  great  deposits  of  iron  ore  and 
graphite  have  long  been  regarded  as  evidence  of  the  presence  of 
organization  early  in  the  Eozoic  JEon.  But  no  organic  forms 
are  known  in  the  Laurentian  or  Huronian  systems  except  Eozoon. 


FIG.  296.— MT.  KEARSARGE  AMONG  THE  WHITE  MOUNTAINS.  SHOWING  FORMS  ASSUMED 
BY  Eozoic  FORMATIONS  IN  PBOCESS  OF  WEATHERING.  BOWLDERS  IN  THE  FORE- 
GROUND. See  section  through  this  mountain,  Fig.  6*2. 


FORMATIONAL   GEOLOGY.  369 

Of  this  enough  has  already  been  said  (pages  318-320).  In  the 
Keweenian  sandstones  of  the  north  flank  of  the  Porcupine  Mount- 
ains Dr.  D.  Houghton  collected,  many  years  ago,  some  remains 
which  appear  to  belong  to  marine  plants,  and  these  the  author 
has  described  as  Palceophycus  arthrophycus  and  P.  articulatus. 
They  are  quite  as  definite  in  form  and  characters  as  any  pre- 
viously described  from  the  Cambrian.  A  representation  of  one 
of  these  is  shown  in  Fig.  295. 

§  3.     The  Cambrian  System. 

1.    Divisions,  Subdivisions,  and  Terms. 
CAMBRIAN    SYSTEM.     [Formations  named  in  natural  order  of 

sequence  downward.     Numbering  is  from  below.] 
III.     Trenton  Group  (4). 

3.  CINCINNATI  STAGE  (4c).  The  Hudson  River  shales  and  slates; 
Lorrain  shales  of  New  York ;  Nashville  Group  of  Tennessee. 

2.  UTICA  STAGE  (4&). 

1.  TRENTON  STAGE  (4a):  (3)  Trenton  limestone;  Galena  limestone  of 

Illinois;    Lebanon  limestone  of  Middle  Tennessee.     (2)   Black 
River  limestone.     (1)  Birdseye  limestone. 
II.     Canadian  Group  (3). 

3.  CHAZY  STAGE  (3c).     Chazy  limestone,  New  York  and  Canada. 

2.  QUEBEC  STAGE   (36).     Canada,   near   Quebec;    shales,    limestones, 

and  sandstones,  Newfoundland.  Part  of  Knox  Group,  Tennes- 
see. 

1.  CALCIFEROUS   STAGE    (3a).     Northern   New  York.     Lower  Mag- 

nesian  limestones  of  Mississippi  valley;  St.  Peters  sandstone, 
Wisconsin  and  Illinois;  Knox  sandstone,  East  Tennessee. 
I.     Primordial  or  Potsdam  Group  (2). 

2.  POTSDAM  STAGE  (2&).     Sandstone  of  Northern  New  York,  of  the 

south  shore  of  Lake  Superior  east  of  Keweenaw  Point,  and  most 
of  that  of  Minnesota  and  Wisconsin.  Chilhowee  sandstone  of 
Tennessee.  Georgia  slates  of  Vermont. 

1.  ACADIAN  or  ST.  JOHN  STAGE  (2a).  St.  John  Group  of  New  Bruns- 
wick; beds  of  St.  Johns  and  elsewhere  in  Newfoundland;  slates 
of  Braintree,  Mass. ;  Ocoee  conglomerate  and  slates  of  Eastern 
Tennessee  and  North  Carolina. 

The  term  "  Cambrian  "  has  been  employed  in  various  senses, 
and  not  unfrequently  as  equivalent  to  what  is  here  denominated 
"Primordial."  The  sense  here  employed  is  that  announced  by 


370  GEOLOGICAL   STUDIES. 

the  Director  of  the  United  States  Geological  Survey  as  the  one 
adopted  for  official  use.  (Report  of  the  Director  for  1881,  page 
xlviii.)  It  is  equivalent  to  "Lower  Silurian"  as  employed  till 
recently  by  most  American  geologists.  The  name  itself  comes 
from  Cambria,  the  ancient  name  of  Wales,  and  was  first  used  by 
Sedgwick  for  fossiliferous  rocks  older  -than  those  by  Murchison 
denominated  "  Silurian,"  from  Silures,  the  designation  of  the 
ancient  inhabitants  of  Wales.  "  Primordial  "  was  employed  by 
Barrande  for  the  lowest  fossiliferous  zone  of  Bohemia.  u  Pots- 
dam "  is  so  named  from  Potsdam,  in  New  York,  and  the  other 
terms  are  geographical  in  their  origin,  requiring  no  explanation, 
it  being  as  a  rule  understood  that  a  locality  or  region  giving  its 
name  to  a  formation  is  one  at  which  the  formation  was  first  sci- 
entifically described  and  defined  with  the  limitations  now  employed 
by  geologists.  (See  Chap.  II,  §  4,  3  (6).) 

2.  Geographical  Extension.  Turning  to  the  Geological  Map, 
we  find  the  Cambrian  strata  generally  resting  against  the  flanks 
of  the  Eozoic  hills  and  mountains.  Thus,  in  Canada  the  valley 
of  the  St.  Lawrence  River  is  underlaid  by  Cambrian  strata.  A 
large  basin,  including  Montreal  and  Ottawa,  indents  the  Eozoic 
area,  and  a  belt  of  these  rocks  sweeps  around  the  Adirondac 
region,  crossing  the  St.  Lawrence  at  Ogdensburg,  bordering  Lake 
Ontario  on  the  north,  passing  under  Georgian  Bay,  rising  above 
the  surface  on  the  chain  of  Manitoulin  Islands,  sweeping  from 
St.  Marie's  River  to  Marquette,  thence  passing  southwestward 
around  the  Michigan- Wisconsin  Eozoic,  and  expanding  south- 
ward over  southern  Wisconsin,  and  northwestward  to  Minne- 
apolis, and  beyond.  In  the  valley  of  the  Red  River  the  Cam- 
brian reappears,  and  stretches  far  toward  the  northwest.  A  large 
part  of  Vermont,  New  Hampshire,  and  Maine  is  occupied  by 
Cambrian  and  Silurian  rocks.  These  strata  come  to  the  surface 
over  a  large  area,  embracing  the  cities  of  Cincinnati,  Madison, 
Frankfort,  and  Lexington  (Ky.);  also  over  another  area  embrac- 
ing Nashville,  Lebanon,  Columbia,  Franklin,  and  Murfreesboro 
in  Tennessee.  An  important  belt  of  Cambrian  and  Silurian  undi- 
vided is  involved  in  the  folds  of  the  Appalachian  Mountains.  In 


FORMATIONAL   GEOLOGY. 


371 


southeastern  Missouri  is  a  considerable  area  stretching  over  into 
Indian  Territory. 

3.  The  Continent  at  the  Beginning  of  the  Cambrian  Age. 
At  the  beginning  of  the  Eozoic  ^Eon  —  that  is,  when  the  sedi- 
ments began  to  be  deposited  which  were  destined  to  form  the 
rocks  of  the  Eozoic  Great  System,  the  regions  now  occupied  by 
those  rocks  must  necessarily  have  been  under  water.  If  there 
were  any  lands  existing  whose  wastage  during  Eozoic  time  sup- 


COBDILLERAN 
10    /  -  I  /LAND  U 


FIG.  297.— NORTH  AMERICA  NEAR  THE  CLOSE  or  THE  Eozoic  J3on.  Based  on  the  latest 
publications  of  the  Canadian  Survey,  and  the  general  views  set  forth  by  King  in  the 
Report  on  the  40th  Parallel  Survey. 

plied  materials  for  Eozoic  sediments,  we  do  not  know  where  they 
were.  They  seem  to  have  been  completely  obliterated.  If  we 
were  to  represent  America  at  the  beginning  of  Eozoic  time,  we 
could  only  represent  an  expanse  of  water.  At  the  end  of  the 
Eozoic  ^Eon,  however,  uplifts  took  place  ;  dry  lands  appeared. 
More  likely,  numerous  uplifts  had  taken  place  during  the  progress 
of  the  Eozoic. 


372  GEOLOGICAL   STUDIES. 

It  will  be  noticed  that  the  continent  of  Cambrian  time  con- 
sisted of  three  great  nuclear  areas,  corresponding  nearly  to  the 
great  Eozoic  areas  already  pointed  out  in  existing  surface  geol- 
ogy. (1)  The  Great  Northern  Area.  This  was  arcuate,  stretch- 
ing from  the  region  of  the  Great  Lakes  northwest  to  the  Arctic 
ocean,  and  northeast  to  the  coast  of  Labrador,  or  perhaps  far  be- 
yond. (2)  The  Seaboard  Area.  This  seems  to  have  stretched 
from  New  Brunswick  southwestward  to  Alabama,  with  a  breadth 
varying  from  75  to  125  miles,  diminished  in  the  latitude  of  New 
Jersey.  There  are  reasons  to  suppose  its  breadth  was  much 
greater  on  the  eastern  side,  and  that  it  continued  over  Nova 
Scotia  and  Newfoundland.  (3)  The  Great  Cordilloran  Area. 
This  spread  uninterruptedly  in  width  from  the  western  border  of 
Great  Plains  into  western  Nevada.  It  was  probably  750  miles  in 
breadth,  but  its  extent  north  and  south  has  riot  been  ascertained. 
This  land  was  a  great  mountain  system,  displaying  lofty  ranges 
made  of  crumpled  strata,  enormous  precipices,  a  result  of  me- 
chanical dislocations,  and  finally  a  type  of  mountain  sculpture  of 
such  broad,  smooth  forms  as  to  warrant  the  belief  that  subaerial 
erosion  had  never  carved  and  furrowed  the  mountain  flanks  with 
the  sharp  ravines  characteristic  of  modern  mountain  topography. 
The  evidences  on  which  these  conclusions  are  based  will  be  par- 
tially disclosed  in  describing  the  results  of  later  geological  actions 
in  the  same  region.  This  massive  belt  of  Eozoic  Cordilleras  deter- 
mined the  limits  of  the  modern  Cordilleras,  and  very  much  of  the 
details  of  their  fundamental  structure. 

This  was  the  beginning  of  the  Cambrian  Age.  This  was  the 
extent  and  configuration  of  the  lands  when  Cambrian  sediments 
began  to  accumulate.  These  were  the  continental  nuclei.  The 
student  will  particularly  notice  that  the  continent  of  the  begin- 
ning of  Cambrian  time  was  formed  of  Eozoic  rocks.  In  that 
sense  we  may  speak  of  it  as  the  Eozoic  continent. 

It  will  be  observed  that  the  mapping  of  an  ancient  continent 
is  much  more  than  the  mapping  of  the  rock  exposures  of  the  cor- 
responding age.  If  it  were  not,  we  might  get  a  map  of  America 
at  the  beginning  of  any  Age  —  the  Carboniferous,  for  instance, 


FORMATIONAL    GEOLOGY.  373 

bv  simplv  taking  a  geological  map  and  coloring  out  all  the  Car- 
boniferous and  newer  formations.  But,  to  illustrate  the  uncer- 
tainty of  such  a  method,  let  us  suppose  the  upheaval  of  the  Sea- 
board Eozoic  took  place  after  the  Carboniferous  Age,  instead  of 
at  the  end  of  the  Eozoic.  Such  may  easily  have  been  the  fact, 
especially  as  we  know  that  was  the  epoch  of  Appalachian  up- 
heaval. The  Appalachian  Eozoic,  therefore,  should  not  appear 
on  a  map  of  the  continent  as  it  was  at  the  beginning  of  the  Car- 
boniferous Age.  There  are  geologists  who  would  leave  it  off ; 
but  we  think  evidences  exist  that  a  great  mass  of  Eozoic  dry 
land  stretched  along  the  place  of  the  present  Atlantic  seaboard, 
as  represented  on  our  chart,  Fig.  297.  As  it  will  be  necessary 
hereafter  to  speak  of  that  land,  we  may  at  once  designate  it  the 
Seaboard  Land. 

4.  Cambrian  Rocks  and  Minerals.  By  reference  to  the 
Table  at  the  beginning  of  this  Section  it  will  be  seen  that  the 
best  known  formation  at  and  near  the  base  of  the  Cambrian  is 
the  Potsdam  Sandstone.  This  formation  varies  from  friable  to 
hard.  It  is  generally  somewhat  coarse-grained,  and  free  from 
argillaceous  matter.  Its  color  is  grayish,  or  reddish,  or  mottled. 
The  student  should  fix  his  attention  upon  this  fundamental  mem- 
ber of  the  Cambrian.  It  may  be  well  to  refer  here  to  the  Cycle 
of  Sedimentation,  explained  on  page  268.  Often  the  Potsdam 
Sandstone  rests  directly  on  the  Huronian  or  Laurentian.  This 
relation  is  well  shown  in  Fig.  107,  where  S  is  the  Potsdam  Sand- 
stone ;  as  also  in  Fig.  55,  where  P  is  the  sandstone  and  E  the 
underlying  Eozoic.  Fig.  38  illustrates  the  same;  and  this  may 
be  considered  a  section  across  the  Adirondac  region,  c  being  the 
Potsdam  Sandstone  resting  on  the  eroded  stumps  of  the  Eozoic 
gneisses  and  schists.  Tracing  the  Potsdam  Sandstone  thence 
along  the  border  of  the  Cambrian  lying  nearest  the  Eozoic,  we 
find  it  in  Wisconsin  lying  horizontally  upon  the  ruggedly  eroded 
surface  of  the  Huronian.  Fig.  298  is  a  very  interesting  illustra- 
tion of  the  contact  between  the  two.  The  Potsdam  Sandstone 
lines  the  south  shore  of  Lake  Superior  from  the  Sault  to  Ke- 
weenaw  Point,  and  forms  the  celebrated  scenery  of  the  "  Pictured 


374 


GEOLOGICAL   STUDIES. 


Rocks.  On  the  west  of  Keweenaw  Point  most  of  the  sandstone 
belongs  to  the  Keweenian;  but  at  Bayfield  and  at  the  Apostles' 
Islands  the  horizontal  sandstone  is  Potsdam.  The  formation  out- 
crops in  the  Black  Hills  of  Dakota,  surrounding  the  Eozoic 
nucleus.  It  is  extensively  developed  along  the  Appalachian 
chain  —  the  slates  and  sandstones  attaining  a  thickness  of  3,300 
feet.  In  East  Tennessee  sandstones  and  shales  several  thousand 
feet  thick  are  described  by  Safford  —  Chilhowee  sandstone  rest- 
ing on  Ocoee  conglomerates,  sandstones,  and  micacous,  talcose, 
and  chloritic  slates.  These  enter  into  the  Unaka  Range,  as  shown 
in  Fig.  33.  The  formation  is  known  in  the  Big  Horn  Mountains, 
at  the  head  of  Powder  River,  along  the  Wahsatch,  Teton,  Madi- 
son, and  Gallatin  Ranges,  also  in  Central  Nevada  and  other  regions 
of  the  Far  West.  The  face  of  a  Potsdam  cliff  on  the  Upper  Mis- 
sissippi is  shown  in  Fig.  30. 


FIG.  298.  —  SECTION  IN  SAUK  COUNTY,  WISCONSIN,  SHOWING  THE  CONTACT  BETWEEN 
THE  POTSDAM  SANDSTONE  AND  THE  HURONIAN  QUARTZITE.  (Chamberlin.)  £, 
Baraboo  River;  7>,  Devil's  Nose;  W,  Wisconsin  River,  separating  Sank  from  Colum- 
bia County;  a,  North  Q.nartzite  Range;  6,  South  Quartzite  Range;  d,  Potsdam  Sand- 
stone; 61  f,  upper  portions  of  Potsdam  Sandstone;  g,  Lower  Magnesian  Limestone; 
h,  Drift.  This  is  the  Quartzite  referred  to,  page  363. 

The  Canadian  Group  represents  the  approach  of  limestone- 
making  conditions,  but  not  their  full  advent.  The  strata  of  the 
East  range  from  a  calcareous  sandstone  below,  to  an  arenaceous 
limestone  above  —  the  Chazy.  These,  in  the  Montreal  basin,  un- 
dergo a  large  development,  and  constitute  an  argillo-calcareous 
group  (the  "Quebec")  of  local  importance.  In  the  Mississippi 
valley,  the  "Lower  Magnesian  Limestone"  holds  position  here. 
This  is  a  buffish,  coarse,  or  granular  limestone,  well  developed  in 
southern  Missouri  and  along  the  Mississippi  north  of  Dubuque. 
A  common  appearance  presented  by  these  two  formations  in  the 
banks  of  the  Mississippi  is  shown  in  Fig.  299.  The  usual  erosion 


FORMATIONAL    GEOLOGY. 


375 


of  the  underlying  sandstone  is  shown  in  Fig.  26,  which  also  shows 
oblique  laminations  —  more  clearly  shown  in  Fig.  195. 

In  the  valley  of  the  Upper  Mississippi,  the  Lower  Magnesian 
Limestone  is  succeeded  by  a  whitish  friable  sandstone  known  as 
the  St.  Peters  Sandstone,  which  attains,  in  places,  a  thickness  of 
200  feet.  It  is  commonly  regarded  as  a  western  representative 
of  the  Chazy  formation.  In  truth,  however,  the  Calciferous, 
Canadian,  and  Chazy,  all  together,  occupy  the  interval  held  by 
the  St.  Peters  Sandstone  at  the  West. 


FIG.  299.— BLUFFS  ON  THE  UPPER  MISSISSIPPI  NEAR  PRAIRIE  DU  CHIEN.  CAMBRIAN 
ROCKS.  The  Lower  Ledge  is  Potsdam  Sandstone,  and  the  Upper,  the  Magnesian 
Limestone.  (D.  D.  Owen.) 

The  central  and  characteristic  mass  of  the  next  Group  is  cal- 
careous—  the  great  Trenton  Limestone,  named  from  Trenton  Falls 
on  the  East  Canada  Creek  in  Central  New  York.  It  stretches 
along  the  middle  of  the  Cambrian  belt  of  strata  as  formerly 
traced,  into  the  Upper  Mississippi  region,  and  northward  past 
Winnipeg,  The  Galena  Limestone  of  Illinois,  Wisconsin,  and 
Iowa  is  the  upper  part  of  the  Trenton.  Its  thickness  in  the 
great  Montreal  basin  is  800  feet;  in  the  Mississippi  valley,  100  to 
200  feet;  in  the  Appalachians  it  amounts  to  2,000  feet.  The 


376 


GEOLOGICAL    STUDIES. 


Cincinnati  or  Hudson  River  formation  is  a  calcareo-argillaceous 
continuation  of  the  Trenton. 

Other  regions  where  the  Trenton  and  Cincinnati  limestones 
are  favorably  exposed  are  Watertown,  N.  Y.,  in  the  banks  of  the 
Black  River;  the  north  shore  of  the  Manitoulin  Islands;  the  west 
shores  of  Green  Bay  and  Little  Bay  de  Noquet;  southwestern 
Wisconsin  and  northwestern  Illinois,  and  some  parts  of  eastern 
Pennsylvania.  The  entire  Cambrian  strata  of  Nevada  are  re- 
ported by  Hague  7,000  feet  thick,  and  include,  from  below,  the 
Prospect  Mountain  Quartzite  and  Limestone,  the  Secret  Canon 
Shale,  the  Hamburg  Limestone,  and  the  Hamburg  Shale.  The 
Pogonip  Limestone,  next  in  order,  probably  embraces  the  Quebec 
and  Trenton  formations.  The  Cambrian  strata  of  the  Wahsatch 
region  are  reported  by  King  12,000  feet  thick. 

5.    Erosion  Features.    The  weathering  of  the  Cambrian  rocks 

in  Wisconsin  and 
Minnesota  has 
resulted  in  many 
remarkable  forms. 
Figs.  30  and  32 
have  been  cited.  In 
Fig.  300  the  "  Hor- 
nets' Nest,"  the  un- 
derlying sandstone, 
as  in  other  cases, 
has  worn  away, 
leaving  the  Mag- 
nesian  Limestone 
overhanging.  In 
other  cases  enor- 
mous towers  are 

left  standing  in  the 
FIG.  300.— THE  "HORNETS'  NEST,"  WISCONSIN.  EROSION  OF  •  -,  ,  /.  •,  • 

CAMBRIAN  ROCKS.    (Chamberlin)  mlds*     °f     a     Plaln» 

showing  how  exten- 
sively formations  have  been  swept  away.  Fig.  301  is  an  example 
of  this  kind  in  Dakota  county,  Minnesota.  Here  the  isolated 


FORMATIONAL    GEOLOGY. 


377 


column  is  over  19  feet  high  above  the  base,  which  is  itself  25£ 
feet  high,  making  the  whole  outlier  44  feet  7  inches  above  the 
sandy  plain.  Much  pictur- 
esque scenery  results  from 
erosion  of  the  Cambrian 
rocks.  The  "  Pictured  Rocks" 
of  Lake  Superior  are  in  the 
Potsdam  Sandstone.  The 
"Dalles"  of  the  Wisconsin, 
Fig.  29,  are  in  the  same 
formation.  The  "Great 
Chasm  of  the  Au  Sable  "  in 
northern  New  York  is  cut  in 
the  Potsdam.  The  Trenton 
Limestone  is  the  occasion  of 
numberless  waterfalls,  some 
of  which,  like  Trenton, 
Glenn's  and  Minnehaha, 
have  become  classic.  The  "High  Falls"  of  the  Hudson  at 
Lucerne  are  partly  in  the  Potsdam  Sandstone. 

The  examination    of   a  section   along   the  Mississippi  River, 
somewhat  like  that  in  Fig.  302,  shows  that  the  Cambrian  sedi- 


G-  301. — "  CASTLE  ROCK,"  MINNESOTA.   OUT- 
LIER or  CAMBRIAN  ROCKS.    (Photograph.) 


a  a  a  b 

FIG.   302.— GENERALIZED    SECTION   ALONG   THE  VALLEY   OF   THE  UPPER  MISSISSIPPI. 

CAMBRIAN  ROCKS,    a,  Eozoic  rocks.     6,  Potsdam  Sandstone,  c,  Lower  Magnesian 
Limestone,     d,   St.  Peter's  Sandstone.     <?,  Trenton  Limestone. 

ments  were  deposited  on  a  deeply  eroded  surface  of  Huronian 
rocks,  constituting  what  has  been  explained  as  a  break  (page 
263).  Erosions  take  place  above  sea  level  or  a  little  below  it. 
This  Huronian  surface  seems,  therefore,  to  have  been  dry  land  for 
a  long  period,  after  its  upheaval,  and  before  the  epoch  of  the  Pots- 
dam Sandstone.  During  that  interval,  sediments  were  accumu- 


378  GEOLOGICAL   STUDIES. 

lating  in  other  regions.  That  is,  before  the  Potsdam  epoch,  and 
after  the  close  of  the  Eozoic,  some  other  formation  unrepresented 
in  the  Northwest  —  unless  the  Keweenian  fill  the  gap  —  was  pro- 
duced. This  intervening  formation  is  found  at  several  points  in 
the  East,  and  is  known  as  the  Acadian  Stage,  consisting  chiefly 
of  slates,  so  far  as  known.  The  Acadian  Stage  is  recognized 
also  in  the  Wahsatch  and  Great  Basin  regions.  The  Potsdam, 
therefore,  was  not  laid  down  over  the  Northwest  until  after  a 
subsidence.  In  other  words,  a  map  of  the  continent  at  the  be- 
ginning of  Cambrian  time  must  show  more  land  than  the  present 
exposures  of  Eozoic  rocks. 

A  similar  history  appears  to  have  been  undergone  in  the 
broad  Cordilleran  region  which  we  have  mapped  as  land  at  the 
beginning  of  Cambrian  time.  After  undergoing  vast  sub-aerial 
erosions,  during  which  marine  sediments  were  accumulating  else- 
where, a  great  subsidence  took  place,  and  the  region  became  an 
archipelago.  This  was  before  the  opening  of  Cambrian  time,  for 
we  find  the  oldest  Cambrian  sediments  deposited  horizontally  in 
the  deep  valleys  of  that  ancient  wasted  surface.  The  entire 
Cambrian  series  was  built  up  in  horizontal  sheets,  and  the  Cordil- 
leran mountain  slopes  were  slowly  buried.  The  same  order  of 
events  continued  through  the  Silurian,  Devonian,  and  Carbonifer- 
ous ages.  The  horizontal  Palaeozoic  strata  abut  against  the 
ancient  slopes;  and  in  one  case  at  least,  according  to  King,  they 
rise  30,000  feet  along  a  mountain  acclivity. 

The  "Cincinnati  Swell,"  so  called,  is  an  upswelling  of  the 
strata  causing  dips  east  and  \vest  from  Cincinnati,  as  shown  in 
Fig.  303.  The  oldest  rocks  are  exposed  in  the  bed  of  the  Ohio 
River  and  in  the  amphitheatre  of  hills  surrounding  the  city. 
Following  the  river  downward  or  upward,  we  reach  outcrops  of 
formations  successively  higher  in  the  series,  and  soon  rise  to  the 
Coal  Measures.  Underneath  the  Trenton  Limestone,  beneath  the 
bed  of  the  river,  lies  the  Potsdam  Sandstone,  which  has  been  actu- 
ally reached  in  boring  an  artesian  well  at  Columbus.  The  hills 
about  the  city  are  formed  of  the  thin-bedded  limestones  and  shales 
of  the  Cincinnati  Group.  In  central  Tennessee,  rocks  of  the  same 


FORMATIONAL   GEOLOGY.  379 

age  are  similarly  brought  to  light  by  erosion  (see  Fig.  33),  but 
with  less  of  a  swell  in  the  strata.  The  fossiliferous  limestones, 
clays,  and  shales  of  the  suburbs  of  Cincinnati  are  reproduced  in 
the  hill  slopes  and  river  bluffs  of  Nashville. 


li  fedcb  a  bcdeg  i 

FIG.  303.— SECTION  ACROSS  THE  CINCINNATI  SWELL.  C,  Cincinnati,  a,  6,  Cambrian;  c, 
Silurian;  d,  Devonian;  e,  Waverly;  /,  Carboniferous  Limestone;  g,  Equivalent  of 
Carboniferous  Limestone  on  the  easterly  side;  h,  Illinois  Coal  Field;  /,  Appalachian 
Coal  Field. 

6.  Organic  Remains.  The  Cambrian  rocks  generally  are 
well  stocked  with  relics  of  the  life  of  the  Age.  For  the  Potsdam 
Sandstone,  the  Upper  Mississippi  valley  is  the  best  collecting 
ground.  For  the  Trenton  and  Cincinnati  formations,  northwest- 
ern Illinois,  southwestern  Wisconsin,  northeastern  Iowa,  and 
southeastern  Minnesota  are  prolific  regions  None,  however, 
have  yielded  a  greater  abundance  of  good  fossils  than  the  Cin- 
cinnati and  Nashville  areas.  The  former  includes  Richmond 
and  Madison,  Ind.,  and  Lexington  and  Frankfort,  Ky. ;  the 
latter,  Lebanon,  Columbia,  Franklin,  and  Murfreesboro.  At  all 
the  points  named,  the  surface  of  the  ground  and  the  banks  of  the 
streams  are  strewn  with  fossil  remains  surprisingly  well  preserved. 
Scarcely  less  abundant  or  excellent  are  the  fossils  found  along 
the  western  shores  of  Green  Bay,  and  the  north  shore  of  Drum- 
mond's  Island,  in  Lake  Huron.  Along  the  Black  River,  in  New 
York,  at  Trenton  Falls,  and  in  Centre  county,  Pennsylvania,  are 
also  rich  deposits.  In  central  Nevada,  the  Pogonip  and  Hamburg 
ridges  are  found  fruitful  in  fossils. 

The  study  of  these  remains  shows  that  with  the  dawn  of  the 
Palaeozoic  ^Eon,  life  was  exceedingly  abundant  in  the  sea;  but 
neither  land  animals  nor  plants  are  indicated,  save  some  probable 
tree  trunks  from  the  Cincinnati  region.  In  respect  to  rank,  these 
animals  ranged  over  all  the  classes  of  invertebrates.  The  Trilo- 
bites,  already  sketched  (page  323),  were  highest  in  rank,  and  most 


380  GEOLOGICAL   STUDIES. 

conspicuous  in  the  Primordial  Period,  and  continued  throughout. 
Cephalopods  of  the  type  of  Orthoceras  were  perhaps  equal  in 
importance,  and  were  certainly  dominant  in  prowess.  Of  these-a 
sketch  has  also  been  given  (page  326).  It  is  noteworthy  that  forms 
indicating  much  complication  and  differentiation  in  structure 
come  from  a  horizon  as  low  as  the  Calciferous,  implying,  perhaps, 
that  simpler  forms,  still  undiscovered,  had  been  in  existence  dur- 
ing periods  still  more  remote.  Among  humbler  forms  were 
Crinoids,  beautiful  creatures  which  rooted  themselves  in  the  sub- 
marine soil,  and  grew  like  tiny  animated  palms.  These  have  also 
been  sketched  (page  324).  But  besides  these  types  were  others 
which  played  important  roles  in  the  plan  of  life  and  the  pro- 
cesses of  sedimentation.  Coral  makers  of  the  type  of  Polyps 
were  not  conspicuous,  except  Favistella  and  Streptelasma,  Figs. 
122-4,  but  coral  makers  of  the  type  of  Bryozoa  were  extremely 
abundant  during  the  Trenton  Period.  Individual  animals  were 
extremely  small,  but  they  combined  in  large  numbers,  and  secret- 
ed coral  masses  from  one  to  eight  inches  in  diameter.  Brachio- 
pods  may  be  particularly  mentioned  as  beginning  their  geological 
history  in  forms  related  to  Lingula,  Strophomena,  and  Orthis 
biforata.  These  have  been  already  described  and  illustrated 
(Studies  XXXIII  and  XXXIV).  Zygospira  modesta  (Fig.  178), 
Orthis  subquadrata  (Figs.  166,  171),  Strophomena  alternata 
(Figs.  191,  192),  and  Orthis  biforata  (Fig.  163),  are  widespread 
and  characteristic  species.  The  particular  features  of  Palaeon- 
tology, however  interesting  or  important,  must  here  be  passed 
over,  to  be  taken  up  in  a  more  advanced  course. 

The  exuberance  of  marine  life  at  an  age  so  remote  that,  aside 
from  Eozoon,  by  some  denied,  it  seems  to  represent  the  very  first 
act  in  life's  drama,  is  a  great  fact  which  may  well  astonish  and 
prompt  to  speculation.  We  must  remember  that  remoteness 
reduces  the  perspective  of  the  Cambrian  to  a  seeming  point  of 
time,  while  it  was  undoubtedly  measured  by  hundreds  of  thou- 
sands of  years.  We  may  bear  in  mind,  also,  that  the  wonderful 
diversification  of  Cambrian  types,  even  from  the  beginning,  may 
possibly  have  been  progressing  during  that  long  Huronian  . 


FORMATIONAL    GEOLOGY.  381 

all  traces  of  whose  organization  have  been   obliterated   by  the 
physical  vicissitudes  of  our  planet. 

§  4.     The  Silurian  System  ("Tipper  Silurian "  of  Authors). 

1.  Divisions,  Subdivisions,  and  Terms. 
III.     Lower  Helderberg-  Group  (7). 
II.     Salina  Group  (6). 

1.  Niagara  Group  (5). 

3.   NIAGARA  STAGE  (5c).     (2)  Niagara  Limestone ;  (1)  Niagara  Shale. 

2.   CLINTON  STAGE  (5&). 

1.   MEDINA  STAGE  (5a).     (2)  Medina  Sandstone;  (1)  Oneida Conglom- 
erate. 

The  Silurian  System,  named  from  Silures,  the  ancient  people 
of  Wales,  was  intended  by  Murchison  to  embrace  all  the  fossil- 
iferous  rocks  under  the  Devonian.  The  progress  of  discovery 
having  extended  downward  our  knowledge  of  such  rocks,  Sedg- 
wick  bestowed  the  name  Cambrian  on  those  which  he  regarded 
as  underlying  the  Silurian,  as  originally  known  to  Murchison; 
while  the  latter  designated  them  Lower  Silurian.  Aside  from 
other  considerations,  convenience  requires  a  single  designation 
for  every  group  important  enough  to  stand  in  the  relation  of  a 
"  System."  Hence,  with  good  reason,  the  National  Survey  has 
proposed  the  use  of  these  terms  as  here  employed. 

The  other  terms  employed  in  the  above  table  are  all  of  New 
York  origin,  and  require  little  explanation.  The  Helderberg 
Mountains  are  in  eastern  New  York,  south  of  Albany.  The 
Salina  Group,  named  from  its  productiveness  in  salt,  was  origi- 
nally the  "  Onondaga  Salt  Group,"  from  its  supply  of  brines  in 
Onondaga  county. 

2.  Geographical  Extension.     If  we  start  from  the  Niagara 
River,  which  gives  its  name  to  the  most  important  mass  of  the 
Silurian,  lithologically  speaking,  we  find  this  system  stretching 
eastward  in  a  broad  belt  through  central  New  York  to  the  Hud- 
son River.     Northward,  it  spreads  to  Lake  Ontario;  and  south- 
ward, it  stretches  along  the  valley  of  the  Hudson,  bending  in 
southeastern  New  York  conformably  with  the  trend  of  the  Appa- 
lachians,  which  it   follows   as  far  as   Georgia.      Westward  and 


382  GEOLOGICAL    STUDIES. 

northwestward  from  the  Niagara  River,  the  Silurian  belt  stretches 
across  Ontario  to  the  headland  separating  Georgian  Bay  from 
Lake  Huron.  It  forms  the  southern  and  principal  part  of  the 
Manitoulin  Islands,  and  borders  the  northern  and  western  shores 
of  Lake  Michigan,  forming  the  cape  which  divides  Green  Bay 
from  Lake  Michigan,  and  spreading  southward  beyond  Chicago. 
Green  Bay  is  thus  the  counterpart  of  Georgian  Bay.  Each  bay 
is  separated  from  its  lake  by  a  promontory  of  Niagara  Limestone. 
A  belt  of  importance  surrounds  the  Cambrian  area  whose  centre 
is  at  Cincinnati,  and  this  extends  northward  to  include  Sandusky. 
Other  Silurian  strata  are  exposed  around  the  Nashville  Cambrian, 
especially  on  the  west.  Silurian  rocks  are  known  in  Maine,  and 
other  parts  of  New  England;  but  in  some  parts,  and  in  regions 
farther  toward  the  northeast,  they  have  not  yet  been  completely 
discriminated  from  the  Cambrian  and  Devonian. 

Throughout  the  whole  extent  of  the  Silurian,  the  Niagara 
Limestone  is  the  great  and  salient  feature.  A  little  acquaintance 
with  the  physical  features  of  the  country  will  enable  one  to  trace 
this  formation  by  means  of  the  quarries,  ledges,  and  escarpments 
which  everywhere  accompany  it  ;  and  when  the  place  of  this 
limestone  is  known,  it  may  be  understood  that  the  higher  groups 
lie  on  the  side  away  from  the  older  formations  —  that  is,  Cam- 
brian and  Eozoic. 

3.  The  Continent  at  the  Beginning  of  Silurian  Time.  Dur- 
ing the  Cambrian  Age  there  occurred  in  northeastern  America  a 
succession  of  uplifts  of  the  sea  bottom;  and  in  consequence  new 
belts  of  territory  were  added  to  the  Great  Northern  Land  repre- 
sented in  Fig.  297.  Speaking  generally,  the  areas  on  the  geolog- 
ical map  shown  as  Cambrian  rose  above  sea  level  during  the 
Cambrian  Age,  and  at  its  close.  As  in  the  East,  later  geological 
erosions  have  removed  some  portions  of  the  original  Cambrian 
covering  the  Eozoic  nuclei  of  the  land,  we  represent  the  land  at 
the  beginning  of  Silurian  time  as  somewhat  more  extended  than 
the  Eozoic  and  Cambrian  surfaces  on  the  Geological  Map. 

In  the  Cordilleran  region,  on  the  contrary,  the  close  of  the 
Eozoic  was  marked  by  a  subsidence  of  this  entire  continental 


FORMATIONAL   GEOLOGY. 


383 


limb,  for  the  Cambrian  sediments  are  laid  down  over  the  whole 
of  the  ancient  eroded  Eozoic  surface,  with  numerous  island-like 
exceptions.  The  subsidence  continued  through  the  Cambrian, 
but  was  greatest  toward  the  west,  where  the  Cambrian  strata  are 
now  thickest.  The  portion  of  the  land  which  supplied  the  sedi- 
ments was  over  western  Nevada  and  the  extreme  eastern  belt  of 
California.  The  great  Cambrian  ocean  east  of  the  Nevada  land 
was  interrupted  only  by  the  rugged  peaks  of  the  ancient  sunken 


'  FIG.  304.-MAP  OF  NORTH  AMERICA  AT  THE  BEGINNING  or  THE  SILURIAN  AGE. 

continent  of  the  earlier  ./Eon,  some  of  which  are  shown  on  the 
map,  Fig.  304.  Similarly  the  great  Seaboard  Land  appears  to 
have  begun  a  process  of  subsidence,  through  which  it  was  over- 
lapped to  an  unknown  extent  by  Cambrian  and  later  deposits. 

In  consequence  of  Cambrian  elevations  in  the  Northern  Land 
and  Cambrian  subsidences  in  the  others,  the  Northern  Land  is  now 
enlarged  on  all  its  borders,  and  has  a  belt  of  Cambrian  sediments 
encircling  it  on  the  southern  side,  and  probably  to  a  limited 
extent  around  the  Hudson's  Bay  border  also.  But  the  Seaboard 


384  GEOLOGICAL   STUDIES. 

and  Cordilleran  Lands  having  subsided  at  and  since  the  close  of 
Eozoic  time,  neither  presents  as  large  an  area  as  in  the  map, 
Fig.  297.  The  Cordilleran  Land,  in  fact,  was  reduced  to  an  archi- 
pelago at  the  beginning  of  the  Cambrian  Age,  and  remained  such, 
with  even  diminishing  land  areas,  to  the  beginning  of  the  Silurian 
Age,  as  represented  in  map,  Fig.  304. 

It  is  scarcely  necessary  to  say  that  these  maps  are  merely 
approximate  and  suggestive.  Where  land  areas  subside  they 
carry  out  of  sight  the  visible  evidences  of  subsidence;  and  where 
they  rise  it  is  not  always  possible  to  ascertain  whether  elevation 
attained  was  greater  or  less  than  the  elevation  existing  at  the 
present  time.  Movements  of  the  kind  here  indicated,  however, 
took  place;  and  what  is  shown  by  these  tentative  maps  of  the 
growing  continent  imparts  general  conceptions  which  are  correct. 

4.  Silurian  Rocks  and  Minerals.  The  Orieida  Conglomerate 
at  the  bottom  properly  exemplifies  the  beginning  of  a  new  cycle 
of  sedimentation  (see  page  268) ;  and  the  progress  of  it  is  shown 
in  the  succession  of  the  Medina  Sandstone.  But  these  two  forma- 
tions cannot  be  traced  westward  beyond  middle  Ontario.  The 
West  was  too  remote  from  the  source  of  the  sediments,  which 
was  probably  in  the  decaying  Seaboard  Land;  and  coarse  mate- 
rials are  replaced  by  finer,  mostly  calcareous  deposits.  The  argillo- 
calcareous  strata  of  the  Clinton  Stage  are  seen,  however,  on  the 
Manitoulin  Islands,  and  farther  west  in  Wisconsin  and  Indiana, 
as  well  as  in  Ohio,  Tennessee,  and  other  regions  —  always  not  far 
removed  from  outcrops  of  Niagara  Limestone.  The  Medina  Sand- 
stone is  a  hard,  gritty,  even-bedded,  reddish,  whitish,  or  mottled 
rock,  quite  extensively  quarried  for  building  purposes,  especially 
in  the  vicinity  of  Lockport,  N.  Y.  The  Clinton  formation  em- 
braces, westward,  thick-bedded,  fine-textured,  aluminous  lime- 
stones, presenting  a  beautiful  appearance,  but  too  retentive  of 
moisture  for  outdoor  architecture.  By  hard  freezing  the  blocks 
are  shivered  to  fragments.  It  includes  important  beds  of  lentic- 
ular iron  ore  in  the  lower  part,  from  the  Genesee  River  eastward, 
and  forms  valuable  deposits  in  Wisconsin,  eastern  Tennessee, 
and  Nova  Scotia. 


FORMATIONAL   GEOLOGY.  385 

The  Niagara  Limestone  is  generally  a  light  or  dark  gray, 
heavy-bedded  rock,  having  a  semicrystalline  texture.  On  Drum- 
mond's  Island,  and  all  around  the  northern  and  western  shore  of 
Lake  Michigan,  to  Chicago,  the  principal  beds  are  quite  crystal- 
line, but  abound  in  small  crystal-lined  cavities,  which  impair  its 
value  as  a  building  stone.  It  is,  however,  extensively  quarried 
for  building  and  for  lirnemaking,  a  portion  of  the  formation  being 
free  from  the  defect  just  mentioned.  Beds  especially  adapted 
for  building  are  found  in  western  New  York  and  at  Joliet,  La- 
mont,  and  thereabouts  in  Illinois.  The  celebrated  "Athens  Mar- 
ble," so  called,  is  quarried  near  Joliet  and  Lament,  and  was  before 
the  "  great  fire  "  a  favorite  building  material  in  Chicago.  It  re- 
mains in  excellent  repute  at  the  present  time.  Niagara  limestone 
is  extensivelv  quarried  at  Huntington,  Ind.  In  Chicago  and  that 
vicinity  some  strata  of  the  Niagara  limestone  are  quite  saturated 
with  petroleum,  and  many  fruitless  expenditures  have  been  in- 
curred in  the  attempt  to  collect  this  fluid  in  quantities  of  com- 
mercial importance.  (But  see  Part  I,  Study  XXVII.)  It  is  said 
the  first  artesian  wells  of  Chicago  resulted  from  the  ventures  of 
oil  seekers  ;  though  it  is  certain  that  geologists  had  already 
asserted  the  practicability  of  procuring  water,  and  the  impossi- 
bility of  getting  supplies  of  oil. 

The  Salina  Group  consists,  in  Central  New  York,  of  tender, 
clayey  marlites  and  fragile  clayey  sandstones  of  red,  gray,  green- 
ish, yellowish,  or  mottled  colors,  constituting  the  lower  half;  and 
above  these,  calcareous  marlites  and  impure  drab-colored  lime- 
stone, containing  beds  of  gypsum,  followed  by  hydraulic  lime- 
stone. A  vein  or  bed  of  dark-green  serpentine  occurs  in  the 
formation,  in  the  city  of  Syracuse,  on  James  street,  and  a  few 
rods  to  the  south.  The  great  feature  of  this  group  is  the  salt 
aud  gypsum  which  it  affords.  (For  geology  of  Salt  and  Gypsum 
see  Part  I,  Study  XXVI.)  Rock  salt  is  now  known  to  have  a 
wide  distribution  through  the  Salina  in  southwestern  New  York, 
Ontario,  eastern  Michigan,  and  western  Michigan.  At  Marine 
City,  on  the  River  St.  Clair,  it  is  found  over  115  feet  thick,  at  a 
depth  of  1,633  feet  to  1,748  feet  from  the  surface;  and  an  enor- 


386  GEOLOGICAL   STUDIES. 

mous  manufacture  of  salt  has  been  established  by  first  dissolving 
the  rock  salt  by  forcing  down  clear  water  from  the  St.  Clair 
River,  and  afterward  evaporating  the  brine  by  means  of  steam 
pipes.  Rock  salt  is  also  found  of  great  thickness  at  Manistee, 
Ludington,  and  Muskegon,  on  the  west  side  of  the  state.  Near 
Goderich,  Ontario,  126  feet  of  rock  salt  are  found  in  520  feet  of 
strata,  down  to  a  depth  of  1,517  feet.  In  Ontario  rock  salt  is 
obtained  at  a  depth  somewhat  over  a  thousand  feet,  at  various 
points  stretching  from  Kincardine  on  Lake  Huron,  on  the  north, 
to  Dawn,  near  Lake  St.  Clair,  on  the  south.  In  Western  New 
York  rock  salt  has  been  found  at  depths  generally  a  little  over 
1,000  feet  at  various  localities  in  Wyoming,  Livingston,  Ontario, 
Yates,  Seneca,  and  Cayuga  counties  —  that  is,  from  the  centre  of 
Wyoming  county  eastward  to  Aurora,  on  Cayuga  Lake.  The 
salt  bed  ranges  from  70  to  85  feet  in  thickness.  No  rock  salt  has 
been  found  by  boring  at  Syracuse  to  the  depth  of  1,969  feet. 

Gypsum,  also,  is  quarried  extensively  in  Cayuga  county,  New 
York.  It  outcrops  on  the  lake  shore  at  Little  Point  au  Chene,  a 
few  miles  west  of  Mackinac.  The  gypsum  of  Sandusky  Bay,  of 
Cayuga,  and  Ontario,  is  of  the  same  age. 

The  Helderberg  Group  —  originally  Lower  Helderberg — con- 
sists of  a  series  of  shales  and  shaly  limestones  and  proper  lime- 
stones, developed  especially  in  the  Helderberg  Mountains,  but 
extending  westward,  with  diminished  thickness,  to  Syracuse, 
Buffalo,  and  western  Ohio.  It  is  known  also  in  Indiana,  southern 
Illinois,  and  other  Western  States.  The  formation  extends  south- 
ward along  the  Appalachians;  and  is  known  in  Massachusetts, 
New  Hampshire,  Maine,  Nova  Scotia,  and  New  Brunswick.  It 
is  famous  for  its  production  of  hydraulic  limestone,  which  sup- 
plies the  Buffalo  Cement  Works  and  numerous  other  establish- 
ments in  New  York  and  Ohio.  The  formation  also  contains  gyp- 
sum. 

5.  Erosion  Features.  Beginning  again  at  the  Niagara  River, 
near  its  mouth,  a  high  escarpment  is  found,  which  runs  eastward 
parallel  with  the  shore  of  Lake  Ontario.  At  Lockport  the  Erie 
Canal  crosses  it,  giving  occasion  for  the  "locks"  which  give 


FORMATIONAL   GEOLOGY.  387 

name  to  the  city.  At  Rochester  it  is  crossed  by  the  Genesee 
River  at  the  "  Falls."  The  great  gorge  of  the  Niagara  River  is 
cut  back  through  this  escarpment  for  about  seven  miles.  A  fine 
section  of  the  Silurian  strata  may  be  seen  along  the  walls  of  this 
gorge,  and  they  are  shown  in  diagram  in  Fig.  305.  This  diagram 
mostly  explains  itself.  The  lower  part  is  supposed  to  be  joined 
on  at  the  right  hand  extremity  of  the  upper  part.  The  student 
will  be  able  to  trace  the  surface  of  the  water  from  Lake  Ontario 
over  the  Falls  and  Lake  Erie  to  Lake  Michigan  and  Chicago.  At 
Cleveland  is  seen  the  high  bluff  on  the  south  shore  of  Lake 
Erie;  and  here  is  a  break  in  the  diagram,  in  consequence  of 
changes  in  the  direction  of  the  section,  and  in  the  direction  of 
the  dip  of  the  strata.  Other  features  of  the  diagram  will  be 
referred  to  in  connection  with  post-glacial  history. 

The  position  of  the  Falls,  now  150  feet  high,  indicates  to 
what  extent  the  gorge  has  been  excavated  back  from  the  escarp- 
ment. We  see  the  water  precipitated  perpendicularly  over  the 
brink  of  the  thick-bedded  Niagara  Limestone.  The  reaction 
against  the  underlying  shale  results  in  its  erosion.  The  limestone 
thus  undermined  breaks  off  by  piecemeal,  and  thus  the  Falls  re- 
cede at  the  rate  of  about  three  feet  a  year.  Within  thirty  or 
forty  years  the  aspect  of  the  Falls  has  changed  materially. 
Within  the  memory  of  a  generation,  "Table  Rock,"  as  shown  in 
the  cut,  Fig.  306,  was  a  great  curiosity  and  point  of  interest  at 
the  Falls  on  the  Canadian  side.  But  it  has  fallen  into  the  abyss. 
Great  encroachments  have  also  been  made  on  Goat  Island. 

6.  Organic  Remains.  The  life  of  the  Silurian  was,  in  gen- 
eral, a  continuation  of  the  types  of  the  Cambrian.  The  Silurian 
genera  and  species  of  the  Cambrian  families  showed  the  progress 
of  those  changes  which  express  slow  organic  advance.  The  forms 
were  less  archaic,  and  less  removed  from  the  aspects  of  the  mod- 
ern world.  Corals  and  Crinoids  became  more  abundant.  The 
Favosites  family  was  developed  under  multiplied  generic  and 
specific  forms.  Some  of  these  are  illustrated  in  Figs.  144,  145, 
146,  148,  and  149.  Rugose  corals  also  underwent  important  ex- 
pansion, but  their  fullest  development  was  yet  future.  Cham- 


235  n. 


38  ft.  above  L.  Erie 


FIG.  305.— DIAGRAM  OF  THE  STRATA  ALONG  THE  NIAGARA  GORGE,  SHOWING  THE  GEO- 
LOGICAL POSITION  OP  NIAGARA  FALLS  AND  THE  ANCIENT  LEVELS  or  THE  GREAT 
LAKES. 


FORMATIONAL   GEOLOGY. 


389 


bered  Molluscs  diminished  in  numbers  and  in  size;  but  the  coiled 
genera  became  rather  more  abundant.  Other  classes  of  Molluscs 
increased  in  relative  numbers.  Trilobites  were  shrunken  in  num- 
bers and  in  bulk.  One  of  them  is  represented  in  Figs.  229  and 
230,  and  is  to  be  contrasted  with  the  Cambrian  Trilobite,  Fig. 
228.  The  Silurian,  however,  witnessed  the  introduction  of  a  type 
entirely  new.  This  was  the  important  type  of  Vertebrates. 
According  to  the  established  method  of  succession,  they  were 
aquatic  breathers;  they  were  low  in  the  Stem  or  Sub-Kingdom, 
and  were  "comprehensive"  forms,  like  all  primitive  types.  Some 
description  of  them  has  been  given  at  pages  231-235.  Further 
palaeontological  details  must  be  passed  by. 


FIG.  306.— TABLE  ROCK  AT  NIAGARA  FALLS,  AS  IT  WAS. 


§  5.     The  Devonian  System. 

1.    Divisions,  Subdivisions,  and  Terms. 

V.     Catskill  Group  (12),     Catskill  Red  Sandstone   [may  be  Carbon- 
iferous]. 

IV.     Chemung-  Group  (11). 

2.   CHEMUNG  STAGE  (11&), 

1.    PORTAGE  STAGE  (lla), 

III.     Hamilton  Group  (10). 


Erie  Shale  of  Ohio, 


8.   GENESEE  STAGE  (lOc),  Tennessee  Black  Shale. 
of  Ohio. 


Huron  Shale 


aa 


5'  3 

B:  Q 

o<3    3 


390  GEOLOGICAL   STUDIES. 

2.  HAMILTON  STAGE  (10&). 

1.  MARCELLUS  STAGE  (10a),  Marcellus  Black  Shale. 
II.     Corniferous  Group  (9). 

3.  CORNIFEROUS  and  ONONDAGA  LIMESTONES   (9c)   (=  "Upper  Helder- 

berg  Group"). 

2.  SCHOHARIE  GRIT  (95). 

1.  CAUDA-GALLI  GRIT  (9a). 

I.     Oriskany  Group  (8).     Oriskany  Sandstone. 

By  some  the  Oriskany  is  regarded  rather  as  Silurian  than 
Devonian.  Palaeontologically  it  has  some  affinities  with  Niagara 
forms,  and  also  some  Devonian  relations.  The  fauna  is  transi- 
tional, as  it  should  be.  Lithologically,  however,  the  formation  is 
plainly  the  beginning  of  a  new  geological  era. 

The  Catskill,  placed  here  at  the  top  of  the  Devonian,  in 
deference  to  prevailing  usage,  may  very  likely  prove  to  be  the 
basal  group  of  the  Carboniferous  System.  It  is  commonly  re- 
garded as  representing  the  Old  Red  Sandstone  of  Scotland, 
which  is  Devonian,  according  to  most  geologists.  Some  British 
geologists,  on  the  contrary,  regard  the  upper  beds  of  the  Old 
Red  as  Carboniferous;  and  this  is  strongly  evinced  at  Dura  Den 
and  Arran.  If  they  are  so,  and  the  Catskill  finds  its  equivalents 
in  them  —  as  the  fossils  indicate  —  the  Catskill  becomes  Carbon- 
iferous, and  holds  exactly  the  horizon  of  the  Waverly  (as  qualified 
by  the  late  Ohio  survey)  and  Marshall  of  the  West,  which,  on 
independent  palasontological  grounds,  may  perhaps  be  parallel- 
ized with  the  Catskill. 

The  geographical  terms  here  employed  are  derived  from 
localities  in  the  State  of  New  York.  "  Corniferous  "  comes  from 
cornUy  a  horn,  in  allusion  to  the  amount  of  "  hornstone  "  con- 
tained; or,  perhaps,  in  allusion  to  the  horn-shaped  cup  corals 
which  abound.  "  Cauda-galli,"  signifying  cock's  tail,  refers  to  a 
peculiar  fucoid  which  the  formation  contains. 

2.  Distribution  and  Lithological  Features.     The  Oriskany 
Sandstone  is  mostly  a  purely  silicious,  friable,  rough -looking  rock, 
but  is  a  somewhat  inconspicuous  formation,  although  it  accompa- 
nies the  other  Devonian  strata  along  the  Appalachians,  and  into 
Ohio,  Indiana,  and  Missouri,  and    attains   a  thickness   of  250  to 


FORMATIONAL    GEOLOGY.  391 

300  feet  in  southern  Illinois.  A  formation  commonly  known 
throughout  the  West  as  the  "Black  Shale"  —  a  black,  bitumin- 
ous, argillaceous  shale  —  is  a  very  persistent  and  characteristic 
part  of  the  Hamilton  Group.  Without  much  doubt,  it  is  the 
equivalent  of  the  Genesee  Shale  of  New  York.  The  Marcellus 
Shale  is  a  very  similar  formation,  with  some  interstratified  lime- 
stones, and  extends  as  far  west  as  the  Detroit  River,  and  perhaps 
into  Ohio.  The  rocks  of  the  Chemung  Group  are  a  bulky  and 
conspicuous  mass  of  greenish,  yellowish,  and  buffish  shaly  sand- 
stones and  variously  colored  shales,  becoming  in  Ohio  and  Michi- 
gan essentially  a  series  of  clays  and  argillaceous  shales.  They 
represent,  therefore,  a  continuation  of  the  shaly  conditions  begun 
with  the  Genesee  Shale,  and  constitute  with  that  formation  a 
stratigraphical  series  which  is  physically  a  unit,  and,  therefore,  in 
Michigan  was  designated  the  "Huron  Group."  The  Chemung 
rocks  (including  the  Portage)  have  a  very  large  development  in 
southern  New  York  and  Pennsylvania,  but  are  deficient  south 
and  west  of  the  Ohio. 

The  most  conspicuous  and  most  persistent  lithological  feat- 
ure of  the  Devonian  is  the  great  central  calcareous  mass.  This 
is  made  up  primarily  of  the  united  Onondaga  and  Corniferous 
limestones;  but  in  Ohio,  Michigan,  and  other  western  states,  as 
far  as  Iowa,  the  Hamilton  formation,  predominantly  argillaceous 
in  New  York  and  Ontario,  becomes  predominantly  calcareous; 
and  since  the  Marcellus  Shale  is  generally  wanting  in  the  West, 
the  Hamilton  and  Corniferous  limestones  unite  in  one  great  cal- 
careous formation.  In  Ohio  and  Indiana  the  formations  between 
the  Corniferous  and  Niagara  limestones  are  also  wanting;  so  that 
the  Hamilton,  Corniferous,  and  Niagara  limestones  are  all  brought 
together,  forming  what  the  older  writers  termed  the  "  Cliff  Lime- 
stone "  (Fig.  307).  The  separation  of  all  these  is  now  easily 
effected  by  means  of  their  fossils. 

The  great  limestone  mass  of  the  Devonian  forms  a  conspicu- 
ous feature  in  the  landscape,  traceable  by  a  line  of  quarries  and 
ledges  all  the  way  from  central  New  York  to  Iowa.  Its  position 
is  not  far  from  the  centre  of  the  belt  marked  as  Devonian  on  the 


392 


GEOLOGICAL   STUDIES. 


Geological  Map;  but  west  of  Ohio  the  limestones  make  up  the 
principal  part  of  this  belt. 

The  economical  products  of  the  Corniferous  are  materials  for 
quicklime  and  for  building  purposes.  For  .the  latter  it  is  much 
employed  in  central  and  western  New  York,  and  in  northern 
Ohio  and  Ontario.  Large  accumulations  of  petroleum  are  found 
in  the  crevices  and  caverns  of  the  Hamilton  Limestone  in  Ontario. 
The  Corniferous  Limestone  is  very  often  found  saturated  with 
dark  petroleum,  but  no  permanent  supplies  of  importance  have 
been  obtained  from  it.  The  most  considerable  yields  have  been 
found  at  Tilsonburg,  Ont.,  and  Terre  Haute,  Ind.  Petroleum 
also  accumulates  abundantly  in  the  Chemung  sandstones  of 
southern  New  York  and  western  Pennsylvania.  (See  Part  I, 
Study  XXIX.)  For  building  purposes  these  sandstones  possess, 
generally,  insufficient  coherence.  Beds  probably  the  equivalent 
of  the  Chemung  constitute  the  "  Kidney  Iron  Formation "  of 
Branch  County,  Michigan. 

NEW    YOEK 

Gel:      __ 

L_ mr      i         ~~    i 

Hamilton          — '-      —     — -» -i —    ~r- 


FIG.  307.— CONSTITUTION  OF  THE  "C'Lirr  LIMESTONE"  or  OHIO. 

3.  Erosion  Features.  The  Corniferous  Limestone  has  been 
the  theatre  of  great  erosion  along  the  course  of  certain  rivers, 
and  around  the  shores  of  the  Great  Lakes.  In  central  New 
York  many  deep  valleys  like  that  of  Onondaga  Creek,  south  of 
Syracuse,  have  been  excavated  in  the  Corniferous  and  Onondaga 
formations.  In  the  vicinity  of  the  Straits  of  Mackinac  the  Cor- 
niferous limestone  has  been  eroded  on  a  grand  scale.  A  lofty 


FORMATIONAL    GEOLOGY. 


393 


barrier  once  separating  the  basins  of  Lake  Huron  and  Lake 
Michigan  has  been  cut  through.  In  the  midst  of  the  passage 
rises  the  Island  of  Mackinac  to  the  height  of  350  feet.  On  three 
sides  the  island  is  bounded  by  precipitous  walls  about  150  feet 
high.  On  the  west,  on  the  Upper  Peninsula  of  Michigan,  is  a 
headland  known  as  Rabbit's  Back,  which  is  the  continuation  of 
the  limestone  of  Mackinac  Island.  On  the  south,  the  main  land 
of  the  Lower  Peninsula  presents  a  similar  but  less  elevated  prom- 
ontory, and  the  exposure  of  the  formation  stretches  toward  the 
east  and  the  west.  The  whole 
island  is  manifestly  a  relic  and 
memorial  of  the  destructive  pow- 
er  of  the  elements.  The  waves 

FIG.  308. 

have  beaten  its  precipitous  walls,    SECTION     SOUTHEAST     AND     NORTHWEST 

and   wasted    them    away    at    un-       THROUGH    MACKINAC    ISLAND,     a,  Old 

_..  Fort  Holmes;  6,  Sugar  Loaf;  c,  Robin- 

equal  rates.     Fissures,  purgato-      Folly.  ^  Rabbit's  Back,  on  the  Upper 

ries,     and     caverns     have     been       Peninsula;  e,  Round  Island  ;/,  Conglom- 
j     ±  j-jy  j.i  critic   stratum:  m.  surface  of  the  lake. 

opened  at  dmerent  stages  in  the 

height  of  the  waters.     In  one  place,  a  veritable  natural  bridge 

stands  swung  at  an  elevation  too  high 
for  the  eroding  agent  to  reach  (Fig. 
309).  On  the  main  plateau  of  the  isl- 
and rises  Sugar  Loaf  (Fig.  310)  134  feet 

above  the 
plain.  The 
pinnacle  of 
the  island  was 
the  site  of  Old 
Fort  Holmes. 
(Compare  also 
Fig.  305.) 

The  axis  of 
Lake   Huron 


FIG.  309. 
'ARCHED  ROCK,M  MACKINAC  ISL- 
AND.   Corniferous  Limestone. 


FIG.  310. 

'SUGAR  LOAF, M  MACKINAC  ISL- 
AND.   Corniferous   Limestone. 


of  the  Corniferous  limestones. 


crosses 

nally  the  trend 
The  lake  shores  present  many 


394  GEOLOGICAL   STUDIES. 

cases  of  bold  erosion.  Off  Thunder  Bay  Island,  in  fair  weather, 
one  may  look  down  a  subaqueous  cliff  ninety  or  one  hundred 
feet,  into  a  dark  abyss  of  water.  Near  Louisville  was  once  a 
fall  in  the  Ohio  River,  over  a  ledge  of  Corniferous  limestone. 
The  retreat  of  these  "Falls"  has  reduced  them  to  mere  rapids; 
but  they  still  present  a  fine  example  of  erosion.  Other  instruct- 
ive examples  may  be  seen  on  the  Mississippi  River  at  Rock 
Island,  and  at  the  head  of  Little  Traverse  Bay  of  Lake  Michi- 
gan. 

4.  Organic  Remains.  In  the  invertebrate  realm  we  find  the 
coral  type  exceedingly  augmented  during  the  Devonian.  Great 
coral  reefs  appear  to  have  been  built  up  somewhat  as  in  modern 
times.  One  of  these  is  exposed  at  the  "  Falls  of  the  Ohio." 
This  has  been  a  favorite  collecting  ground  for  more  than  a  gen- 
eration. Here  abound  corals  of  the  types  of  the  Rugosa  and 
Tabulata,  the  study  of  which  was  explained  in  Part  I,  Studies 
XXX-XXXII.  A  similar  reef  exists  at  the  head  of  Little  Trav- 
erse Bay,  near  Petoskey.  Here  the  type  of  Stromatoporidce 
undergoes  a  remarkable  development;  and  this  is  repeated  in  the 
same  formation  on  the  opposite  side  of  the  state,  at  Thunder 
Bay,  and  the  vicinity.  Stromatoporidce  make  up  a  large  part  of 
the  reef-like  masses  forming  the  Hamilton  limestone  of  these 
regions.  This  interesting  type  seems  to  have  attained  its  culmi- 
nation in  the  Hamilton  and  Corniferous  periods.  We  have 
devoted  some  space  to  its  exposition  and  illustration  in  the  last 
chapter.  See  Figs.  223-7. 

Examples  of  Devonian  corals  are  shown  in  Figs.  130-143; 
also  147-158. 

Some  characteristic  Devonian  Brachiopods  are  seen  in  Figs. 
161,  162,  165,  166,  168,  170,  172,  174,  177,  179,  180,  184. 

Some  characteristic  Devonian  Fishes  are  illustrated  in  Figs. 
241-247. 

A  majority  of  the  fossils  furnished  by  the  Drift  of  the  north- 
western states  are  of  Devonian  age. 


FORMATIONAL   GEOLOGY.  395 

§  6.      The  Lower  Carboniferous  System. 

1.  Divisions,  Subdivisions,  and  Terms. 

II.  Carboniferous  Limestone,  or  Mississippi  River  Group  (13). 
Mountain  Limestone. 

4.  CHESTER  STAGE  (13d).  (2)  Kaskaskia,  or  Upper  Archimedes  Lime- 
stone; (1)  Pentremital  Limestone. 

3.  ST.  Louis  STAGE  (13c).  St.  Louis  Limestone.  Part  of  Silicious 
Group,  Tenn. 

2.  KEOKUK  STAGE  (13&).  Keokuk  Limestone.  Part  of  Silicious  Group, 
Tenn. 

1.  BURLINGTON  STAGE  (13a).  Burlington  Limestone  (?)="  Michigan 
Salt  Group." 

I.  Marshall,  or  Waverly  Group  (12).  "Kinderhook  Group,"  of  111.; 
"Yellow  Sandstones,"  of  Iowa;  "Chouteau"  and  "Lithograph- 
ic" Limestones,  of  Mo.;  "Goniatite  Limestone,"  of  Rockford, 
Ind.;  "  Silicious  Group  "  (lowest  beds),  Tenn.  As  before  stated, 
the  Group  may  be  the  western  equivalent  of  the  prior-named 
"Catskill." 

The  Lower  Carboniferous  Series  is  frequently  designated 
"  Sub-Carboniferous "  ;  but  as  this  term  necessarily  signifies 
"  under  the  Carboniferous,"  it  is  etymologically  inadmissible, 
since  the  Series  is  universally  recognized  as  a  part  of  the  Carbon- 
iferous. The  term  Carboniferous  signifies  coal-bearing;  in  fact, 
however,  the  great  coal-bearing  strata  in  many  parts  of  the  world 
are  Mesozoic,  or  even  Caenozoic. 

The  numerous  local  designations  of  the  lower  Group  origi- 
nated in  the  fact  that  for  years  these  rocks,  in  Ohio,  Iowa,  Mis- 
souri, and  Michigan,  were  regarded  as  the  western  equivalent  of 
the  Chemung;  until,  in  some  regions,  they  were  seen  to  be  so 
clearly  Carboniferous  that  more  thorough  examinations  were 
instituted.  During  the  discussion,  the  formation  in  each  state  — 
not  yet  known  to  be  the  same  formation  —  received  a  local  desig- 
nation. 

The  great  limestone  formation  of  the  Lower  Carboniferous 
Series  may  appropriately  be  designated  the  Carboniferous  Lime- 
stone, since  in  the  whole  Carboniferous  System  it  is  by  far  the 
most  important  and  most  persistent  limestone  mass.  In  the 


396  GEOLOGICAL   STUDIES. 

United  States,  it  underlies  chiefly  the  great  valley  of  the  middle 
Mississippi;  and  hence  the  present  writer  once  suggested  for  it 
the  "Mississippi  River  Group."  In  many  parts  of  Europe  it 
enters  into  the  formation  of  mountains,  and  is  commonly  known 
as  the  Mountain  Limestone. 

2.  Distribution  and  Lithological  Features.  The  Marshall, 
or  Waverly  Group,  consists  in  Michigan  and  Ohio  of  rusty,  or 
yellowish,  mostly  friable,  sandstones,  becoming,  in  the  lower 
beds,  grayish  or  bluish,  and  at  bottom,  decidedly  argillaceous. 
Locally,  some  of  the  beds  are  quite  calcareous  and  finely  cement- 
ed. In  Michigan,  the  formation  outcrops  at  intervals  in  a  broad 
belt  passing  through  the  central  southern  counties,  and  extend- 
ing northwest  into  Ottawa  county,  and  northeast  to  the  lake 
shore  (Point  aux  Barques),  in  Huron  county.  In  Ohio  it  stretches 
from  the  lake  shore,  in  the  vicinity  of  Cleveland,  southward 
across  the  state  to  Waverly  and  the  Ohio  River.  In  eastern 
Iowa  the  formation  is  yellowish  or  buffish,  friable,  and  in  the 
lower  part,  argillaceous.  In  Missouri  it  is  mostly  argillo-calca- 
reous.  In  southern  Illinois,  Kentucky,  and  Tennessee,  it  is  in 
part  a  dark,  laminated,  silicious  shale. 

Some  of  the  purely  arenaceous  beds  afford  superior  gritstones, 
of  which  the  Berea  (Ohio)  and  Huron  (Mich.)  grindstones  are 
examples.  They  are  equally  in  request  for  building  and  flagging- 
purposes.  The  famous  bluestone,  or  freestone,  of  Cleveland 
and  vicinity,  and  regions  southward  to  Waverly,  belongs  here. 
The  fine  Nova  Scotia  freestone  is  probably  of  the  same  age. 

The  Carboniferous  Limestone  Group  is  almost  exclusively 
calcareous.  The  St.  Louis  member,  however,  is  apt  to  be  cherty, 
especially  in  Kentucky  and  Tennessee,  where  it  forms  the  most 
characteristic  part  of  the  "  Silicious  Group "  of  Safford.  This 
cherty  limestone  is  spread  out  over  a  large  area  through  central 
Kentucky,  and  thence  into  Tennessee.  It  forms  the  rugged 
"  Knob  Region  "  of  those  states.  In  Michigan,  the  limestone  is 
of  the  St.  Louis  and  Keokuk  subdivisions;  in  southern  Ohio  it  is 
the  Chester  and  St.  Louis.  In  Michigan,  however,  is  a  member 
of  the  series  underneath  the  limestone,  which  is  argillaceous,  with 


FORMATIONAL   GEOLOGY. 


397 


thin  intercalated  calcareous  sheets,  and  heavy,  persistent  beds  of 
beautiful  gypsum,  quarried  very  extensively  near  Grand  Rapids, 
and  also  on  the  opposite  side  of  the  state,  near  Tawas  Bay,  at 
Alabaster.  This  is  the  "  Michigan  Salt  Group."  It  is  probably 
of  the  same  age  as  the  gypsum  beds  of  New  Brunswick,  which, 
like  the  Michigan  gypsum,  belong  to  the  upper  group  of  the 
Lower  Carboniferous. 

The  succession  and  conformability  of  the  Lower  Carbonifer- 
ous strata  are  shown  in  the  instructive 
bluff  at  Burlington,  Iowa,  a  section  of 
which  is  shown  in  Fig.  311.  In  spite 
of  the  complete  conformability  of  the 
upper  and  lower  strata,  the  distinct- 
ness of  the  two  groups  is  evinced  by 
the  strong  contrast  in  the  organic 
remains. 

Limestones  of  Carboniferous  age 
occur  at  many  points  throughout  the 
remote  West;  but  in  many  cases  they 
belong  to  the  Upper  Carboniferous; 
in  other  cases,  their  precise  age  has 
not  been  ascertained.  Limestones  of 
the  Lower  Carboniferous  have  been 
identified  in  the  Elk  Mountains  of 
western  Colorado  ;  the  Wind  River 
Mountains  of  Wyoming;  at  Old  Baldy, 
Montana,  near  Virginia  City  (Chester 
Limestone);  at  Fort  Hall,  Idaho  (St. 
Louis  Limestone);  in  the  Wahsatch  y 
and  Oquirrh  ranges,  Utah  (St.  Louis 
Limestone),  and  in  the  Eureka  district  FIG.  311.— SECTION  OF  THE  BLUFF 

Of   Nevada,  where   the   Diamond   Peak      AT  BURLINGTON,  IOWA.    LOWER 

CARBONIFEROUS  ROCKS.     (C.  A. 
Quartzite  is  3,000  feet  thick,      rroba-     white.)   i  toe,  "Yellow  Sand- 

blv    some    of    the     western     exposures  stones";    7  to  8,    Carboniferous 

J  /.     i       TIT        i     n  Vt  Limestone;    9,  Drift;    R,  Mean 

embrace  strata  of  the  Marshall  broup.  Heightof  the  River;  A,  Division 

Carboniferous    limestone   occurs,   also,  between  the  two  Groups. 


398  GEOLOGICAL   STUDIES. 

in  the  Gray  Mountains,  California,  near  Ross'  Ranch,  1,000  feet 
thick  (?  St.  Louis),  and  at  Pence's  Ranch,  eighty  miles  south, 
according  to  Whitney. 

The  distribution  of  the  calcareous  and  fragmental  materials  of 
the  Lower  Carboniferous  illustrates  the  principle  heretofore 
explained,  that,  with  increase  of  distance  from  the  source  of  the 
sediments,  the  depositions  become  less  fragmental,  and  more 
calcareous.  The  Carboniferous  Limestones  which,  in  southwest- 
ern Illinois,  are  1,000  to  1,300  feet  thick,  become  attenuated, 
eastward,  to  ten  or  twenty  feet  in  southeastern  central  Ohio; 
while  in  the  Appalachian  region,  3,000  feet  of  soft  reddish  shales 
and  sandstones  (the  Umbral  Series)  occupy  the  horizon  of  the 
Mississippi  limestones.  On  the  contrary,  the  Marshall,  or  frag- 
mental group,  which  is  100  to  200  feet  thick  in  Illinois,  and  640 
feet  in  Ohio,  is  represented  in  the  Appalachians  by  2,000  feet  of 
coarse,  grayish  conglomerates  and  sandstones  (the  Vespertine 
Series),  passing  down  into  red  sandstone,  commonly  regarded  as 
of  Catskill  age.  Locally,  however,  this  lower  group  contains 
from  eighty  to  eight  hundred  feet  of  limestone. 

At  many  places  in  Pennsylvania  and  Virginia,  the  Vespertine 
Series  contains  beds  of  coal,  one  of  which  is  two  to  two  and  a 
half  feet  thick,  succeeded  in  Montgomery  county,  Virginia,  at 
the  distance  of  thirty  to  forty  miles,  by  another  bed  six  to  nine 
feet  thick,  consisting  of  alternations  of  coal  and  slate.  These 
deposits  are  sometimes  called  False  Coal  Measures.  Lower 
Carboniferous  coal  beds  occur  also  in  Great  Britain. 

In  Nova  Scotia  and  New  Brunswick,  the  Lower  Carboniferous 
consists,  also,  of  two  epochs.  The  lower,  or  Jforton  Series,  is 
made  up  of  red  sandstones,  conglomerates,  and  red  and  green 
marlites,  intercalated  with  thin  seams  of  coal.  The  Albertite 
(page  68)  of  the  Albert  mine  is  contained  in  a  fissure  in  this  series 
in  New  Brunswick.  This  fragmental  group  is  chiefly  developed 
northward  in  the  vicinity  of  the  Eozoic  formations  which  supplied 
the  sediments.  The  upper  series,  called  the  Windsor  Series,  is 
developed  chiefly  southward,  and  as  might  be  expected,  consists 


FORMATIONAL    GEOLOGY. 


399 


mostly  of  limestones   and  marlites,  but  contains,  also,  extensive 
beds  of  gypsum. 

3.  Geography  of  the  Continent  During  the  Lower  Carbon- 
iferous Age.  The  distribution  of  the  sediments  of  the  Lower 
Carboniferous  shows  that  the  Mississippi  Valley  was  the  site  of  a 
great  interior  ocean,  which  opened  freely  southward,  but  on  the 
east  was  bounded  by  the  great  Seaboard  Land  which  had  first 
risen  during  or  at  the  end  of  the  Eozoic  ^Eon,  and  which  was 


FIG.  312. — NORTH  AMERICA,  NEAR  THE  BEGINNING  OF  THE  CARBONIFEROUS  AGE. 

bordered  on  the  west  by  a  belt  of  shallow  sea,  occupying  the 
position  in  which  the  Appalachian  chain  was  destined  to  be 
uplifted  in  a  future  age.  This  border  was  the  theater  of  active 
fragmental  deposition.  The  materials  were  derived  from  the 
wastage  of  the  contiguous  Seaboard  Land,  and  perhaps  a  conti- 
nental shore  lying  farther  toward  the  northeast.  The  slow  sink- 
ing of  the  sea  bottom  (perhaps  accompanied  by  a  sinking  of  the 
Seaboard  Land)  caused  the  accumulations  to  proceed  to  the 
extent  revealed  in  the  heavy  beds  of  the  Umbral  and  Vespertine 


400  GEOLOGICAL   STUDIES. 

series  of  eastern  Pennsylvania.  The  remote  interior  was,  mean- 
while, the  scene  of  crinoidal  life  and  calcareous  depositions.  In 
the  Mississippi  valley,  the  fine  arenaceous  beds  of  the  Marshall 
Group,  resting  on  the  Devonian,  stretch  toward  northern  Iowa. 
The  northern  limits  of  the  overlying  Burlington  Limestone  are 
200  miles  more  southward,  and  the  northern  borders  of  the  other 
divisions  of  the  Carboniferous  Limestone  are  fixed  successively 
more  to  the  south.  This  shows  a  gradual  southward  encroach- 
ment of  the  land.  During  the  St.  Louis  epoch  there  was  a  tem- 
porary subsidence,  but,  as  a  rule,  the  higher  members  of  the 
Group  are  southern  in  position,  while  the  lower  are  northern. 

In  the  midst  of  this  interior  ocean  the  great  Cincinnati  swell 
rose  as  a  peninsula,  stretching  southward  from  the  Michigan 
border,  at  which  it  bifurcated,  sending  one  branch  toward  Onta- 
rio and  New  York,  and  the  other  toward  Wisconsin  —  in  each 
case  to  join  the  mainland.  The  greater  part  of  the  Michigan 
peninsula  was  an  inland  salt  sea,  like  the  modern  Euxine,  in 
which  geological  history  proceeded  somewhat  independently,  but 
yet  under  the  same  terrestrial  conditions  as  determined  the  gen- 
eral tenor  of  physical  and  organic  progress. 

The  Cordilleran  region,  which  was  a  broad,  mountainous  belt 
at  the  end  of  the  Eozoic,  and  then  subsided  to  receive  the  sedi- 
ments of  the  Cambrian  and  Silurian,  continued  to  sink  during 
Devonian  and  Carboniferous  time.  The  source  of  the  sediments 
was  the  Nevada  land;  and  the  greatest  subsidence  was  westward. 
The  whole  Palaeozoic  series  attains,  according  to  King,  a  thick- 
ness of  1,000  feet  in  the  eastern  part  of  the  Cordilleran  region, 
32,000  feet  in  the  Wahsatch  region,  and  40,000  feet  at  the  extreme 
western  Palaeozoic  limit,  longitude  117°  30'.  At  the  close  of  the 
Palaeozoic,  the  uppermost  sheet  of  the  Carboniferous,  extending* 
from  the  Nevada  Palaeozoic  shore  eastward  to  the  Great  Plains, 
was  only  interrupted  by  a  few  island-like  granite  peaks,  which 
were  above  the  level  of  deposition  —  the  great  mass  of  Eozoic 
topography  having  by  that  time  been  completely  buried.  Tongues 
and  belts  of  these  Carboniferous  strata  stretched  west  of  the 
main  Nevada  shore,  as  indicated  by  the  positions  of  gulfs  and 


FORMATIONAL   GEOLOGY.  401 

bays  then  penetrating  even  into  the  limits  of  the  present  states 
of  California  and  Oregon. 

4.  Erosion  Features.     Like  all  limestones,  the  Carboniferous 
limestone  has  suffered  greatly  through  the  agencies  of  solution 
and  erosion.     The  silicious  or  cherty  nature  of  the  Warsaw  and 
St.    Louis   divisions  has   caused   very  unequal  weathering,    and 
hence  a  very  rugged   aspect  in  the   landscape  of  the  so  called 
"  Knobs."      The   St.    Louis  division   is   especially  abundant   in 
caverns   in  Indiana,  Kentucky,  and   Tennessee.     These  may  be 
regarded  as  elating  back  to  the  beginning  of  the  Mesozoic  ^Eon. 
Whatever  fissures  may  have  been  produced  by  movements  of  the 
earth's  crust,  have  been  continually  enlarged  in  later  times  by 
percolating  waters.     The  Mammoth  Cave,  a  plan  of  which  has 
been  given  in  Fig.  209,  is  probably  the  greatest  result  known  of 
cave-making  agencies. 

Many  of  these  caves  have  contained  extensive  deposits  of 
various  salts,  especially  of  a  lime  saltpetre,  or  nitrocalcite.  The 
great  limestone  formation  in  the  Cumberland  Table  Land  contains 
hundreds  of  "  nitre  caves,"  which,  in  the  early  part  of  the  present 
century,  especially  in  1812-1814,  were  industriously  worked  for 
nitrocalcite  for  the  manufacture  of  nitre. 

5.  Organic  Remains.     The   organic  remains  of  the  Lower 
Carboniferous  indicate  a  fauna  that  differed  in  important  particu- 
lars from  that  of  the  Devonian.     The  type  of  corals   was   less 
luxuriant,  both  in  respect  to  the  tribes  of  Cup  Corals  (Tetraco- 
ralla)  and  those  of  Tabulate  Corals  (Hexacoralla),  but  especially 
the  latter.     The  compound  cup  coral,  Lithostrotion,  however,  is 
a   common   and  characteristic  species  of  the  widely  spread  St. 
Louis  Limestone;  and  simple  cup  corals,  indeed,  remained  in  con- 
spicuous   abundance.      But    the    crinoidal    type    expanded    to    a 
splendid  culmination  (see  description,  page  324).     The  limestone 
of  the  upper  part  of  the  bluff  at  Burlington,  Iowa  (Fig.  311),  is 
in  some  of  its  beds  composed  chiefly  of  the  broken  stems  and 
the  calices  of  crinoids.     This  locality  is  classical  ground  for  the 
palaeontologist.     Mr.  Charles  Wachsmuth  has  collected-  here  355 
species  belonging  to  44  genera.     Crawfordsville,  Ind.,  is  another 


402  GEOLOGICAL   STUDIES. 

productive  locality.  The  state  of  preservation  of  the  crinoids  is 
even  better  than  at  Burlington,  the  rock  being  an  argillaceous 
shale;  but  the  number  of  species  does  not  exceed  100,  according 
to  Professor  D.  A.  Bassett,  who  states  that  several  thousand  speci- 
mens have  been  removed.  The  principal  genera  are  Actinoc'- 
rinus,  Baryc'  rinus,  Cyathoc' rinus,  Dichoc' rinus,  Forbesioc'- 
rinus,  Goniasteroidoc' rinus,  Onychoc' rinus,  Platyc' rinus,  Scaph- 
oc'rinus,  and  Taxoc'rinus  (Bassett).  The  beds  here  are  of  Keo- 
kuk  Limestone.  The  higher  divisions,  also,  from  southern  Illinois 
to  northern  Alabama  and  the  Cumberland  Table  Land,  are  gener- 
ally well  stocked  with  the  remains  of  crinoidal  life.  Fig.  234 
gives  a  view  of  a  crinoid  from  the  W^averlv  group  of  Ohio  — 
the  epoch  of  the  great  expansion  of  the  type  under  its  specially 
Carboniferous  aspect. 

Straight  chambered  shells  were  still  in  process  of  disappear- 
ance; but  the  coiled  Goniatites  and  Nautili  were  very  abundant 
(see  page  326);  and  Lamellibranchs  were  increasing  in  numbers 
and  diversification  —  especially  in  the  earlier  periods.  Brachio- 
pods  were  on  the  decline.  The  old  genera,  Strophomena,  Leptmna, 
Orthis,  and  others,  were  near  extinction.  Spirifera  was  repre- 
sented in  numerous  species,  many  of  large  size,  and  Syringotti '- 
yris  made  its  advent  into  America  and  Europe.  Producta  and 
Chonetes  were  characteristically  abundant.  The  last  of  the 
Trilobites  now  lived,  greatly  dwarfed  in  bulk;  but  higher  Crusta- 
ceans were  taking  their  place.  Fishes  were  in  the  high  career 
of  advancement;  but  none  belonged  yet  to  the  modern  type  of 
Teleosts.  They  were  either  Ganoids  or  Selachians;  and  of  the 
latter,  the  Cestraciont  type  was  peculiarly  prominent.  The  forms 
of  life  here  mentioned  should  be  again  studied  on  pages  331-335. 

§  7.     The  Upper  Carboniferous  System. 

1.    Divisions,  Subdivisions,  and  Terms. 
IT.     Permian  Group. 
T.     Coal  Measures. 
2.    UPPER  COAL  MEASURES. 

1.    LOWER  COAL  MEASURES.  \  '^°wer  Coal  Measures"  of  Rogers. 

Conglomerate  Measures. 


FORMATIONAL   GEOLOGY.  403 

The  term  Permian  is  derived  from  the  province  of  Perm,  in 
Russia,  in  which  a  group  of  strata  of  this  age  was  described  as  a 
"  System."  It  consists,  in  Europe,  of  two  principal  divisions, 
and  hence  is  often  called  the  "Dyas." 

The  details  of  the  stratification  of  the  Coal  Measures  are  not 
identical  at  remote  points;  but  a  general  correspondence  exists 
through  western  Pennsylvania  and  Ohio,  from  which  a  standard 
series  of  formations  has  been  drawn  up,  as  shown  below.  For 
the  parallelisms  of  the  Ohio  coals  I  depend  on  Orton's  recent  and 
important  Report.  In  Indiana,  western  Kentucky,  and  Illinois 
only  a  more  general  correspondence  has  been  traced.  In  regions 
still  more  remote  the  correspondence  is  reduced  to  the  existence 
of  a  series  of  shales,  sandstones,  coal  beds,  occasional  limestones, 
and  one  or  more  considerable  conglomerates  at  or  toward  the 
bottom  of  the  series. 

Standard  Section  of  the   Coal  Measures,  Specially  Suited  to 
Western  Pennsylvania  and  Eastern  Ohio. 

UPPER  COAL  MEASURES.     THICKNESS,  1,700  FEET. 

V.      Upper  Barren  Measures  of  Rogers,  974  ft.,  containing 
6  coal  beds,  8  ft.,  and  having  at  bottom, — 

46.    Waynesburg  Sandstone. 
IV.    Upper  Coal  Measures  of  Rogers  =  Monongahela  Series. 

45.   Waynesburg  Coal,  6  ft.  (I),  XXI. 

44.    Pittsburgh  Sandstone,  Shales,  and  Limestones. 

43.   Pittsburgh  Coal,  8  ft.  (H),  Cumberland,  Md.,  Pomeroy 

Bed,  Ohio,  Primrose  bed  of  Anthracite.  XX. 

III.   Lower  Barren  Measures  of  Rogers  =  Pittsburgh  Series. 

42.    Upper  Pittsburgh  Limestone,  2  ft. 

41.    Lower  Pittsburgh  Limestone,  5  ft. 

40.   Morgantown  Sandstone,  45  feet  =  1st  "Oil  Sand,"  Dunk- 
ard's  Creek. 

39.   Elk  Lick  Coal,  3  ft.  (F?)  (G?),  XIX. 

38.   Elk  Lick  Limestone,  2  ft., 

37.   Berlin  Coal,  3  ft.  (F?).  XVIII. 

36.    Green  Crinoidal  or  Berlin  Limestone,  2  ft. 

35.   PlattP  Coal,  lift.,  .      XVII. 

34.   Price  Coal,  XVI. 


404  GEOLOGICAL   STUDIES. 

33.   Bakerstown  Coal,  2i  to  4  ft.,  XV. 

32.    Pine  Creek  Limestone,  2  ft. 

31.    Buffalo  Sandstone  =  Upper  Mahoning  S. 

30.    Brush  Creek  Limestone. 

29.   Brush  Creek  Coal,  XIV. 

28.  Mahoning  Sandstone,  40  to  80  ft.,  and  Shale  50  ft.  Lower 
Mahoning.  ?  Anvil  Rock  S. ;  Kurlew  S.,  Ky.=  2d  ''Oil 
Sand,"  Dunkard's  Creek  —  the  principal  reservoir.  A 
"  gas  rock." 

LOWER  COAL  MEASURES.     THICKNESS,  642  FEET. 

II.     Lower  Coal  Measures  of  Rogers.    Thickness,  392  ft.  = 

Allegheny  Series. 
FREEPORT  GROUP. 

27.   Upper  Freeport  Coal,  4  ft.  (E),  Muskingum  County  and 

Valley.     "  Mammoth  Bed "  of  Anthracite,  XIII. 

26.   Upper  Freeport  Limestone,  3  ft.     White  L.,  Ohio. 

25.    Upper  Freeport  Sandstone,  30  ft.     Butler  S. 

24.  Lower  Freeport  Coal,  2  ft.  (U).  Unreliable  in  Pennsyl- 
vania, XII. 

23.    Lower  Freeport  Limestone,  2|  ft.     Butler  L. 

22.    Lower  Freeport  Sandstone  and  Shale,  75  ft.     Freeport  S. 
KITT ANNING  GROUP. 

21.   Upper  Kittanning  Coal,  H  to  3  ft.  (C1).     Blacksmith 

Vein,  XI. 

20.  Middle  Kittanning  Coal,  3  to  6  feet.  Little  known  in 
Pennsylvania.  Coshocton,  Ohio ;  Great  Vein  of  Hocking 
Valley,  Ohio,  X. 

19.   Lower  Kittanning  Coal,  2i  ft.  (C).     "Kittanning"  of 

Rogers,  IX. 

18.    Kittanning  Clay,  10  ft.     New  Brighton  Fire  Clay. 

17.   Kittanning  Sandstone,  42  ft.     Lower  Kittanning  S. ;  Indus- 
try S,  Ohio. 
CLARION  GROUP. 

16.   Ferriferous  Limestone  and  Buhrstone  Ore,  1  to  15  and  20  ft. 

15.   Upper  Clarion  Coal,  2  ft.     Scrubgrass;  Canfield  Cannel,     VIII. 

14.   Lower  Clarion  Coal,  H  ft.  (B).     Clarion  Coal,  VII. 

13.  Putnam  Hill  Limestone.     Not  in  Pennsylvania. 

12.   Brookville  Coal,  2  ft.  (A).     Mahoning  Valley  Coal.  VI. 

I.  Conglomerate  Measures.  Thickness  in  Ohio,  250  ft.  = 
Serai  Conglomerate  of  Rogers  (No.  XI)  =  Sharon  Coal 
Series  of  Hodge  =  Pottsville  Conglomerate. 


FORMATIONAL   GEOLOGY.  405 

BEAVER  RIVER  GROUP. 

11.    Homewood  Sandstone,  75  to  155  ft.     Serai  Conglomerate. 
Tops  of  Pottsville  Conglomerate;   Piedmont  Sandstone; 
Tionesta  Sandstone ;  Upper  Homewood  Sandstone. 
10.   Tionesta  Coal,  3  ft.,  V. 

9.  Upper  Mercer  Limestone  and  Ore,  2|  ft.  Mahoning  Lime 
stone. 

8.   Upper  Mercer  Coal,  2  to  5  ft.,  IV. 

7.  Lower  Mercer  Limestone  and  Ore,  2$  ft.  Mercer  Limestone ; 
Zoar  L. 

6.   Lower  Mercer  Coal,  21  to  3  ft.     Lower  Porter  of  Rogers,        III. 

5.  Conoquenessing  Sandstone  (Upper),  45  ft.  Lower  Potts- 
ville Conglomerate;  Lower  Homewood  Sandstone;  Mas- 
silon  Sandstone  (part)  in  Ohio  =  1st  "  Mountain  Sand." 

4.    Quakertown  Coal,  3  ft,  (and  Shales),  II. 

3.  Conoquenessing  Sandstone  (Lower),  25  ft.  Massilon  Sand- 
stone (part). 

2.  Sharon  Coal  (and  Shales),  4  to  6  ft.  Block  Coal  of  Ma- 
honing  Valley;  Brier  Hill  Coal;  Massilon  Coal,  I. 

1.  Sharon  Conglomerate,  30  feet.  In  Pennsylvania,  Garland 
Conglomerate  and  Olean  Conglomerate.  In  Ohio,  Ohio 
Conglomerate  part  or  all  —  2d  "Mountain  Sand." 

This  series  is  followed  downward,  in  Pennsylvania,  by  the 
"Shenango  Sandstone"  or  "Ferriferous  Fish  Bed,"  (  =  Sub- 
Garland  =  Sub-Olean)  and  the  Meadville  Upper  and  Lower  Lime- 
stones, belonging  to  the  Lower  Carboniferous. 

Most  of  the  standard  terms  in  the  foregoing  table  are  from 
Pennsylvania  Geology.  The  capital  letters  in  parentheses,  fol- 
lowing the  names  of  coal  seams,  were  applied  by  Lesley  to  the 
Pennsylvania  series  above  the  Serai  Conglomerate.  Serial  num- 
bers for  the  entire  Coal  Measures,  based  on  the  latest  determina- 
tions of  the  Pennsylvania  and  Ohio  Surveys,  here  follow  the 
names  of  the  coal  beds  in  Roman  capitals. 

It  has  generally  been  considered  that  the  Coal  Measures 
proper  consisted  of  the  formations  above  what  is  here  designated 
Conglomerate  Measures;  and  that  the  "Conglomerate  "  or  "  Mill- 
stone Grit  "  of  the  English  formed  a  natural  boundary.  But  it 
is  found  that  the  supposed  basal  Conglomerate  lacks  the  uni- 
formity and  persistence  and  constancy  of  stratigraphical  position 


406  GEOLOGICAL   STUDIES. 

once  assumed;  and  that  the  system  of  coal  beds,  even  including 
limestones,  continues  below  the  conglomerate  horizon,  giving, 
along  the  Appalachian  belt,  some  of  the  thickest  and  best  de- 
posits—  sometimes  known  as  "  False  Coal  Measures."  It  is  found, 
also,  that  the  only  coal  of  Arkansas  is  subconglomerate.  In  Ten- 
nessee the  Sewanee  coal  bed  is  230  feet  below  the  Conglomerate, 
and  371  feet  above  the  Carboniferous  Limestone.  For  such  rea- 
sons geologists  (Lesley,  J.  J.  Stevenson,  Orton)  incline  to  treat 
as  one  group  the  entire  series  of  strata,  both  above  and  below 
the  "  Conglomerate." 

The  "  Conglomerate,"  being  an  ambiguous  term,  was  replaced, 
in  1860,  by  the  present  writer,  with  the  geographical  designation 
"Parma  Conglomerate."  Subsequently,  for  similar  reasons,  it 
received,  in  Canada,  the  name  Buenaventure  Conglomerate. 

The  student  will  understand  that  the  Table  does  not  enumer- 
ate the  complete  sequence  of  strata,  but  only  the  salient  forma- 
tions, which  possess  economic  or  stratigraphical  importance,  and 
serve  as  landmarks  in  the  grand  succession  of  deposits. 

2.  Distribution.  The  coal-producing  Coal  Measures  are  con- 
fined, in  America,  to  the  region  east  of  the  Rocky  Mountains. 
The  locations  of  the  various  coal  fields  will  be  learned  from  the 
Geological  Map  :  (1)  The  Appalachian  Coal  Field,  having  a 
length  of  875  miles,  and  a  breadth  ranging  from  30  to  180  miles, 
with  an  area  of  59,000  square  miles.  (2)  The  Eastern  Interior, 
or  that  of  Illinois,  Indiana,  and  northwestern  Kentucky,  47,000 
square  miles.  (3)  The  Western  Interior,  or  that  of  Iowa,  Mis- 
souri, Kansas,  Arkansas,  and  Indian  Territory,  18,000  square 
miles.  (4)  The  Michigan,  6,700  square  miles.  (5)  The  Rhode 
Island,  500  "square  miles.  (6)  The  Acadian,  or  that  of  Nova 
Scotia  and  New  Brunswick,  18,000  square  miles. 

In  the  Rocky  Mountains  and  beyond,  Coal  Measure  limestones 
are  known  to  occur  in  Montana,  Wyoming,  Colorado,  Utah, 
Nevada,  and  California;  but  all  the  coal  west  of  Omaha  to  the 
Pacific  coast  is  Mesozoic  or  Caenozoic. 

The  accompanying  Coal  map  of  Pennsylvania  and  Ohio  shows 
the  interrupted  attenuations  of  the  six  Pennsylvania  bituminous 


FORMATIONAL   GEOLOGY. 


407 


basins,  and  indicates  the  distribution  of  the  anthracite  coal  of 
eastern  Pennsylvania.  Their  names  are  as  follows:  (1)  Southern 
or  Schuylkill  Basin  and  Mine  Hill,  146  square  miles;  (2)  Shamo- 
kin  (50),  Mahonoy  (41),  and  Lehigh  (37)  Basins,  1528  square 
miles;  (3)  Wyoming  and  Lackawana  Basin,  198  square  miles. 
Total  anthracite  area,  472  square  miles.  The  conglomerates  of 
the  lower  portion  of  the  Coal  Measures  generally  extend,  as  in 
northeastern  Ohio,  considerably  beyond  the  areas  covered  by  the 
coal  beds.  They  often  lie  in  huge  cuboidal  blocks  dislocated 


FIG.  313.— COAL  MAP  or  PENNSYLVANIA  AND  OHIO.    Coal  Areas  in 
Black.    Dotted  line  shows  northern  limit  of  the  basal  Conglomerate 
in  Ohio.    Mesozoic  Red  Sandstone  in  broken  horizontal  lines.    1. 
Schuylkill.Anthracite  Field.    2.  Shamokin,  Mahonoy,  and  Lehigh  Ba- 
sins.   3.  Lackawana  and  Wyoming  Basin.    Z>,  Great  Dike.    F,  Fault. 
NOTE.— Several  great  faults  run  parallel  with  the  Appalachian  folds.    One  remark- 
able fault  extends  along  the  Great  Valley  of  Virginia  by  the  ridge  called  North  Mountain 
see  Fig.  92),  and  into  Pennsylvania.     Another  one,  of  20,000  feet,  occurs  near  Chambers- 
burg,  bringing  Cambrian  strata  up  to  a  level  with  upper  Devonian. 

from  the  formation,  as  in  the  southern  counties  of  New  York, 
where  they  form  "Rock  Cities"  and  "Ruined  Cities."  The 
same  may  be  seen  along  the  western  border  of  the  eastern  coal 
field  of  Kentucky,  and  along  the  brow  of  the  Cumberland  Table 
Land,  where  masses  as  large  as  dwelling  houses  have  been  broken 
off  and  rolled  down  the  steep  escarpment. 

3.  Kinds  of  Rocks.  The  Conglomerate  series  presents  gen- 
erally a  conspicuous  conglomeritic  mass,  which  has  in  southern 
New  York  a  thickness  of  25  to  60  feet.  In  the  anthracite  region 
it  is  1,000  to  1,500  feet  thick,  thinning  westward  to  250  feet  on 


408  GEOLOGICAL   STUDIES. 

the  Ohio  River,  including  all  the  associated  strata.  The  nature 
of  this  change  in  thickness  indicates  the  eastern  origin  of  the 
detrital  materials  in  the  great  Seaboard  Land,  as  we  believe. 

The  Coal  Measure  strata,  including  the  Conglomerate  series 
as  well,  embrace  shales,  clays,  limestones,  sandstones,  and  beds 
of  iron  ore  and  coal.  Something  of  their  arrangement  may  be 
learned  from  the  Table  on  page  403.  It  must  be  understood, 
however,  that  this  is  not  a  full  enumeration  of  the  strata.  Rogers 
enumerated,  for  instance,  one  hundred  important  strata  and  for- 
mations above  the  Homewood  Sandstone,  and  left  200  feet  at  the 
top  of  the  Measures  unspecified.  Every  bed  of  coal,  as  a  rule, 
is  understood  to  be  underlaid  by  fire  clay.  It  is  often  accom- 
panied by  shales  and  sandstones.  Thus,  the  Upper  Freeport 
Coal  has  underneath,  50  feet  of  sandy  shales.  The  Lower  Free- 
port  Coal  has  above,  4  feet  of  bituminous  shale,  and  below,  2  feet 
of  fire  clay.  The  Lower  Kittanning  Coal  is  followed  downward 
by  the  Kittanning  clay,  8  feet;  sandy  shales  or  sandstone,  25 
feet;  buhrstone  iron  ore,  1  foot;  Ferriferous  Limestone,  15  feet; 
Scrubgrass  coal,  2  feet;  shales,  etc.,  25  feet;  Clarion  Lower  Coal, 
3  feet. 

The  fundamental  order  of  stratification  given  in  the  Table 
has  been  traced  from  western  Pennsylvania  into  Ohio;  but  the 
shales  and  sandstones  are  subject  to  great  variation.  The  coal 
beds  and  the  limestones  are  the  most  persistent  features,  and 
these  are  the  means  of  parallelizing  the  measures  at  remote 
localities.  The  Lower  Mercer  Limestone,  for  instance,  has  been 
widely  used  as  a  geological  guide.  It  is  thin,  but  wonderfully 
persistent.  Its  color  is  dark  blue,  or  almost  black,  with  thickness 
from  one  to  three  feet;  contains  much  iron  and  silica  and  an 
abundance  of  fossils,  and  is  everywhere  overlaid  by  excellent 
iron  ore.  The  Upper  Mercer  Limestone  is  very  similar,  but  less 
uniform,  and  is  also  accompanied  by  iron  ore  and  a  seam  of  coal. 
The  Ferriferous  Limestone  is  the  centre  of  a  group  of  strata, 
comprising,  besides  the  limestone,  the  best  iron  ore,  the  largest 
clay  deposits,  and  several  of  the  most  widely  worked  coal  seams 
of  the  Lower  Coal  Measures.  This  group  of  formations  serves  to 


FORMATIONAL   GEOLOGY.  409 

identify  the  horizon.  The  limestone  is  15  to  20  feet  thick,  pure 
light  gray  above  and  grayish-blue  below,  frequently  with  a  de- 
posit of  buhrstone  at  top,  and  with  this  a  valuable  bed  of  iron 
ore.  The  limestone,  also,  is  full  of  fossils.  This  recurrence  of 
similar  deposits  in  relation  to  successive  limestones  will  be  under- 
stood as  an  aspect  of  the  cycle  of  sedimentation  (page  268). 

The  so  called  "  Mammoth  Bed "  B  has  been  identified  at  the 
following  points:  Leonard's,  above  Kittanning,  Pa.  (3£  feet); 
Mahoning  Valley,  Cuyahoga  Falls,  Chippewa,  etc.,  Ohio;  the 
Kanawha  Salines;  the  Breckenridge  Cannel  Coal  and  other  mines 
in  Kentucky,  the  first  (or  second)  Kentucky  Bed;  the  lower  coal 
on  the  Wabash,  Ind. ;  Morris,  etc.,  111.;  Murphysborough,  111.; 
Clinton,  Mo.  [250  species  of  plants]. 

The  Pittsburgh  Bed,  H,  at  the  following  points:  Cumberland, 
Md.;  Wheeling;  Athens,  Ohio;  the  Pomeroy  Bed,  Ohio;  Mul- 
ford's  in  western  Kentucky,  the  llth  Kentucky  Bed.  This  bed 
underlies  an  area  of  14,000  square  miles. 

The  lowest  coal  beds  are  most  developed  in  the  Appalachian 
region.  In  the  Schuylkill  Basin  we  have  15  coal  seams,  each 
from  3  to  25  feet  thick,  in  all  113  feet  of  coal,  of  which  80  feet 
are  marketable.  In  the  second  and  third  basins  there  are  60  feet 
of  coal.  The  Upper  Coal  Measures  are  more  developed  in  west- 
ern Pennsylvania,  and  relatively  still  more  in  the  states  farther 
west.  The  coal  beds  which  are  anthracite  in  eastern  Pennsylvania 
are  semi-bituminous  in  middle  Pennsylvania,  bituminous  at  Pitts- 
burgh, and  more  bituminous  in  Ohio  and  Indiana.  As  we  go 
westward,  the  Coal  Measure  limestones  grow  thicker,  and,  of  the 
coal  beds,  the  lower  coals  disappear,  and  the  upper  diminish  in 
thickness  and  value. 

The  characteristics  of  the  different  varieties  of  coal  have  been 
given  in  Part  I,  Study  XIII. 

The  Coal  Measure  rocks  in  the  \Vahsatch  Range  consist  of 
Upper  Coal  Measure  limestones,  2,500  to  3,000  feet;  Middle  Coal 
Measure  quartzites,  5,000  to  7,000  feet;  Lower  Coal  Measure 
limestones  (Wahsatch  Limestone)  amounting,  with  Lower  Car- 
boniferous and  Upper  Devonian  limestones,  to  7,000  feet. 


410 


GEOLOGICAL   STUDIES. 


In  the  Eureka  district  of  Nevada,  the  Lower  Coal  Measures 
consist  chiefly  of  heavy -bedded  dark  blue  and  gray  limestone, 
3,800  feet;  followed  upward  by  the  "Weber  Conglomerate," 
2,000  feet.  The  Upper  Coal  Measures  are  light-colored  blue 
and  dark  limestones,  500  feet. 

4.  Geological  Structure.  Beds  of  coal,  being  mere  stratified 
rocks,  have  been  subjected  to  all  the  tilting,  folding,  and  meta- 
morphism  which  have  affected  contiguous  strata.  In  most  parts 


FIG.  314.— SECTION  IN  A  REGION  OF  UNDULATING  COAL  MEASURES. 

of  the  Mississippi  Valley,  the  disturbances  of  the  strata  amount 
seldom  to  more  than  gentle  undulations.  The  coal  beds,  there- 
fore, are  often  quite  continuous  and  uniform.  The  gentle  undu- 
lations, however,  frequently  bring  them  within  reach  of  surface 
erosions,  and  thus  the  continuity  of  a  coal  bed,  or  of  several  beds, 
is  frequently  interrupted,  as  shown  in  Fig.  314,  which  represents 
the  general  position  of  the  coal  strata  in  the  West.  In  Ohio  the 


GOODMAN^S'HILL  LKKTON 


NEW-LISBON       W;BKAVKI 


TELXOW  ca. 


Level  of  L.  Erie 


FIG.  315.— SECTION  FROM  CANFIELD  TO  HAMMONDSVILLE,  FROM  NORTH  TO  SOUTH.  IN  MA- 
HONING  AND  COLUMBIANA  COUNTIES,  OHIO.  (Orton.)  Coal  Seams  numbered  as  in 
the  Table,  page  403. 

Coal  Measures  have  undergone  very  little  disturbance,  as  may  be 
inferred  from  the  section  in  Fig.  315,  taken  in  the  northeastern 
part  of  the  state. 

In  Illinois,  the  Coal  Measures  have  suffered  moderate  dis- 
turbances. The  "Shawnee  Fault"  crosses  the  coal  field  from 
east  to  west  near  its  southern  extremity;  and  another  fault 
crosses  the  whole  length  of  the  coal  field  nearly  north  and  south. 
The  former  crosses  the  Mississippi  River  at  Bailey's  Landing,  in 


FORMATIOtfAL   GEOLOGY.  411 

Missouri.  In  Jackson  county,  Illinois,  it  brings  Devonian  lime- 
stone to  the  surface  at  the  Bake  Oven  and  Bald  Bluff,  on  the 
Big  Muddy,  where  it  stands  on  an  inclination  of  25°.  It  con- 
tinues across  the  state,  and  crosses  the  Ohio  River  near  Shawnee- 
town,  into  Kentucky,  whence  it  continues  eastward  to  Bald  Hill, 
in  Union  county,  and  as  far  as  the  eastern  boundary  of  Hender- 
son county.  The  other  Illinois  axis  of  disturbance  enters  the 
state  in  Stephenson  county,  on  the  north,  intersects  Rock  River 
at  Grand  Detour,  and  the  Illinois  River  at  Split  Rock,  between 
La  Salle  and  Utica,  and  continues  S.  20°  E.  to  the  Wabash 
River,  in  Wabash  county.  It  brings  the  St.  Peters  Sandstone  to 
the  surface  on  Rock  River,  and  the  Lower  Magnesian  on  the 
Illinois.  These,  and  other  smaller  disturbances  which  have  taken 
place  since  the  Coal  Period,  combine  with  erosions  in  breaking 
up  the  continuity  of  the  Coal  Measures  in  Illinois. 


FIG.  316.— SECTION  FROM  THE  GREAT  NORTH  TO  THE  LITTLE  NORTH  MOUNTAIN,  THROUGH 
BORE  SPRINGS,  VA.  (Rogers.)  t,  t,  t,  Thermal  Springs;  77,  Calciferous;  777,  Tren- 
ton; IV,  Cincinnati;  F,  Oneida:  F7,  Clinton  and  Lower  Helderberg;  F77,  Oriskany 
and  Cauda-galli. 

A  still  more  disturbed  condition  of  the  Coal  Measures  is  illus- 
trated in  Figs.  33  and  34.  The  great  folds  of  the  Appalachians 
involve  the  various  beds  of  coal  in  a  complexity  of  structure 
whose  unfolding  has  taxed  the  highest  skill  of  geologists.  Fig. 
316  is  an  example  of  the  shape  into  which  foldings  and  erosions 
have  brought  strata  originally  horizontal  and  continuous.  Fig. 
92  is  another  illustration  of  Appalachian  disturbance.  The 
anthracite  coal  basins  present  a  series  of  valuable  coal  beds  in  an 
extraordinary  state  of  distortion,  which  brings  within  a  given 
surface  area  an  amount  of  coal  which  would  not  be  suspected 
from  the  area  and  the  thickness  of  the  beds.  In  Fig.  317  we 
have  a  section  across  the  east  end  of  the  First,  or  Schuylkill 
Anthracite  Basin,  not  far  from  Mauch  Chunk,  Pa.  It  represents 
a  depth  of  about  2,000  feet,  and  shows  two  of  the  grand  folds  of 


412 


GEOLOGICAL    STUDIES. 


the  Appalachians  (1  and  2),  and  three  intermediate  smaller  ones 
(3,  4,  5). 

It  has  been  said,  in  speaking  of  the  Lower  Carboniferous  Sys- 
tem, that  each  successive  division  in  the  Mississippi  Valley  has 
its  northern  limit,  as  a  rule,  a  little  farther  south.  This  is  evi- 
dence of  progressive  upheaval  northward,  while  the  sedimenta- 
tion was  going  on.  On  the  contrary,  the  succession  of  beds  in 
the  Upper  Carboniferous  indicates  progressive  subsidence  north- 
ward while  the  Coal  Measures  were  in  formation.  Each  succes- 
sive stratum  finds  its  northern  limit  a  little  farther  north,  so  that 


c         b    a 

FIG.  317.- SECTION  NEARLY  NORTH  AND  SOUTH  ACROSS  NESQUEHONING  COAL  BASIN, 
NEAR  MAUCH  CHUNK,  PENNSYLVANIA.  (Macfarlane.)  1,  Locust  Mountain;  2,  Sharp 
Mountain;  3,  Anticlinal,  No.  2  (Rothwell  >;  4,  Anticlinal,  No.  3;  5,  Anticlinal,  No.  4; 
6,  SynclinalB  (Rothwell) ,  7,  Synclinal  0;  8,  Synclinal  D;  9,  Synclinal  E;  10,  Panther 
Creek;  11,  Summit  Hill;  12,  Old  Coal  Quarry. 

COAL  SEAMS.— A  (Rogers),  4  ft. ;  B  (Rogers),  5  ft.;  C,  7),  Small  Seams;  E  (Rogers), 
Mammoth  Bed,  35  ft. ;  F,  Red  Ash,  or  Pencil  Seam,  15  ft. ;  G  (Rothwell),  Brown  Bed, 
5  ft. ;  H,  Small  Upper  Red  Ash  Seams,  a,  Red  Shale  (Catskill) ;  6,  Vespertine  Sand- 
stone; c,  Umbral  Shale;  d,  Serai  Conglomerate;  «,  Slates  and  Sandstones  between 
Coal  Beds. 

not  only  is  the  Carboniferous  Limestone  covered  by  the  Coal 
Measures  in  northern  Illinois,  but  also  the  Devonian  and  Silurian; 
and  the  northern  extremity  of  the  coal  field  even  laps  over  on  the 
Cambrian  of  northern  Illinois.  All  this  is  shown  on  the  Geologi- 
cal Map.  If,  then,  a  section  were  to  be  constructed  through  the 
western  part  of  the  Illinois  coal  'field,  the  northern  portion  of  it 
would  present  the  general  appearance  of  Fig.  318.  Here  the 
older  strata,  E,  C,  S,  were  slowly  rising,  while  the  Lower  Car- 
boniferous sediments  were  accumulating  ;  they  were  sinking 
while  the  Coal  Measures,  M,  were  forming;  and  at  a  subsequent 
epoch  they  have  been  reelevated  to  their  present  position. 


FORMATIOSTAL    GEOLOGY. 


413 


5.  Coal  Mining.  Had  the  coal  beds  been  left  in  the  posi- 
tions in  which  they  were  formed,  our  great  repositories  of  mineral 
fuel  would  have  been  practically  hidden  from  observation.  To 
the  tiltings  and  foldings  of  the  rocks  we  are  indebted  for  the 
disclosure  of  the  buried  stores,  and  for  the  cheapest  method  of 
extracting  them.  Beds  of  coal  often  outcrop  on  hillsides  and  in 


K  D  s  c  E 

FIG.  318.—  IDEAL  SECTION  IN  ILLINOIS,  SHOWING  UNCONFORMITY  BETWEEN  THE  COAL 
MEASURES  AND  OLDER  ROCKS.  jE7,  Eozoic;  (7,  Cambrian:  £,  Silurian;  A  Devonian ; 
K,  Kinclerhook,  followed  by  Lower  Carboniferous  Limestones;  JM,  Coal  Measures. 

ravines  (Figs.  314  and  317),  and  may  be  followed  into  the  earth. 
Their  place  of  outcrop,  however,  is  generally  indicated  only  by  a 
dark  band  along  the  surface,  or  by  coal  fragments  scattered  in 
the  vicinity  —  generally  southward.  When,  by  excavating,  the 
bed  is  struck,  it  is  found  altered,  by  weathering,  to  a  depth  of 
thirty  to  fifty  feet.  Such  coal  is  pulverulent,  or  soft,  browned, 
and  friable,  and  not  marketable.  Fig.  319  shows  the  method  of 
drifting  in  on  a  hillside.  If  possible,  the  spot  is  so  chosen  that 


FIG.  319.— DRIFTING  IN  ON  A  COAL  BED.    a,  Mouth  of  the  Drift. 


the  mine  water  will  flow  out  at  the  entrance.  If  otherwise, 
pumps  must  be  employed.  When  a  region  is  known  to  be  under- 
laid by  coal,  a  shaft  may  be  sunk,  though  no  coal  appears  at  the 
surface.  This  is  illustrated  in  Fig.  320,  which  represents  the 
Upper  Measures  of  western  Pennsylvania  (see  the  Table,  page 
403);  though,  in  fact,  the  surface  of  the  country  is  such  that 


414 


GEOLOGICAL   STUDIES. 


most   mines  in  that  region    are  approached    by    drifts,    or    are 

worked    by    s  I  op  e  s. 

Surface  ^ . ,       The   shaft,    S,  is  the 

means  of  access  to  the 
coal  beds,  W  and  P. 
The  sump,u,  is  sunken 
to  receive  the  water, 
which  is  thence 
pumped  out  by  ma- 
chinery. When  a  coal 
bed,  TPJ  is  reached, 
excavations  are  made 
on  both  sides.  Often 
the  same  shaft  is  sunk 
to  a  second  coal  bed, 
P,  and  occasionally 
even  to  a  third  one. 
Thepassages,  or  gang- 
ways, are  generally 
extended  in  straight 
lines  to  the  limits  of 
the  property,  or  as 
far  as  the  coal  contin- 
ues satisfactory;  and 

other  passages  are  opened  at  right  angles  with  these.  There  are 
different  systems  of  planning  the  underground  work  of  a  mine, 
but  that  most  employed  is  illustrated  in  Fig.  321,  which  shows  the 
plan  of  the  mines  worked  by  a  powerful  and  well  known  com- 
pany in  the  Blossburg  coal  region,  of  Pennsylvania  —  a  region  em- 
bracing, also,  the  celebrated  Morris  Run  and  Fall  Brook  Mines. 

The  plan  of  working  presented  shows  the  condition  of  the 
Arnot  mines  in  1872.  Here  is  a  portion  of  a  coal  bed  about 
1,500  feet  broad  and  1,900  feet  long,  showing  where  the  gang- 
ways have  been  dug  out  for  travel  and  for  ventilation,  and  also 
the  "  rooms  "  or  "  breasts '  from  which  the  coal  has  been  taken. 
It  shows  also  the  large  amount  of  coal  left  for  supporting  the 


„._____..  TT 

FIG.  320 — CONDENSED  SECTION   IN   THE  UPPER  COAL 

MEASURES  OP  PENNSYLVANIA,  SHOWING  METHOD  or 
MINING  THROUGH  A  SHAFT.  W,  Waynesburg  Seam; 
P,  Pittsburgh  Seam;  S,  a  Mining  Shaft;  a,  a,  Down 
Cast;  6,  Up  Cast;  w,  Sump. 


FORMATIONAL   GEOLOGY. 


415 


roof.  These  supports  will  ultimately  be  taken  out  also.  In  some 
regions  the  roof  rock  is  so  fragile  that  the  gangways  have  to  be 
timbered.  Even  then  the  enormous  weight  sometimes  crushes 


mTwr 


B     A 

FIG.  321.— PLAN  OF  THE  MINES  OF  THE  BLOSSBURG  COAL  Co.,  AT  ARNOT,  PA.  SCALE 
400  FT.  TO  THE  INCH.  (After  Macfarlane.)  A,  the  Main  Gangway ;  B,  the  Eeturn 
Air  Course  and  Ventilating  Shaft.  The  light  portions  represent  the  ground  worked 
over  to  1872. 

the  supports,  and  disasters  happen.  The  same  plan  of  mining  is 
pursued  whether  the  mine  is  approached  by  an  adit,  as  shown  in 
Fig.  319,  or  by  a  shaft,  as  in  Fig.  320. 


416 


GEOLOGICAL   STUDIES. 


In  the  anthracite,  and  occasionally  in  bituminous,  coal  regions 
mining  is  done  by  slopes,  which  are  simply  inclined  planes  or  slop- 
ing tunnels  underground,  generally  cut  in  the  coal  seam  to  avoid 
"  dead  rock."  Drifts,  which  are  always  most  economical,  are 
generally  practicable  in  the  bituminous  coal  regions  of  Pennsyl- 
vania, Ohio,  eastern  Kentucky,  Tennessee,  Georgia,  and  Ala- 
bama; but  in  the  less  disturbed  and  less  denuded  regions  of  Illi- 
nois and  Michigan  resort  must  generally  be  had  to  shafts. 

6.  Organic  Remains.  The  coal  itself  affords  abundant  traces 
of  vegetation,  but  generally  they  are  obscure  and  unidentifiable. 
Spores  and  spore  cases  of  Lycopodiuni-\i\HQ  plants  (Lepidoden- 
drids)  are,  however,  extremely  abundant  —  the  spores  appearing 
as  minute  grains.  Vegetable  structure  may  also  be  detected, 
even  in  anthracite,  by  preparing  thin  sections  and  rendering  them 

as  translucent  as  pos- 
sible. The  associated 
shales  are  often  richly 
stocked  with  fronds  of 
ferns  and  fragments 
of  flowerless  plants. 
They  are  closely 
pressed  on  the  surfaces 
of  the  laminae,  and 
preserve  all  the  deli- 
cate structures  of  the 
plant  in  such  perfec- 
tion as  fully  to  reveal 
its  nature.  Remains 
of  plants  are  also  often 
disseminated  through 
the  sandstones ;  arid 
here  occur,  sometimes, 

FIG.  322.— IMPRESSIONS  op  FERNS  ON  COAL  SHALES,  MOR-  considerable  f  rag- 
RIS,  ILL.  Pseudopecopteris  Mazoniana,  Lx.  a,  en-  „,-„*«,  of  tree  trunks 
larged  pinnules  showing  nervation. 

In    some    remarkable 
instances  such  trunks  have  been  found  still  in  an  erect  position, 


FORMATIONAL   GEOLOGY. 


417 


together  with  other  growths  in  their  original  situations,  as  at  the 
Joggins,  in  Nova  Scotia,  Fig.  323.     The  limestones  embraced  in 


FIG.  323. — ERECT  STUMPS  IN   SANDSTONE  OF  THE  COAL  MEASURES  AT  THE  JOGGINS, 
NOVA  SCOTIA,  AVITH  ROOTLETS  IN  THE  UNDERCLAYS.    (Dawson.) 

the  Coal  Measures  contain,  of  course,  the  relics  of  marine  forms 
—  especially  Brachiopods,  Bryozoa,  Crinoids,  and  Fishes.     These 

limestones  and  their  included 
faunae  become  largely  developed 
in  Illinois,  as  at  La  Salle,  and  in- 
crease westward. 

A  synopsis  of   the   classifica- 
tion of  plants  is  given  on  page 


FIG. 


.  —  LIVING  TREE  FERN.     (After 
Brogniart.) 


FIG.  325.— Megaphy turn,  A  COAL 
FERN  RESTORED.  (After  Dawson.) 


305.     The  terrestrial  types  most  abundant  in  the  Coal  Measures 
were  already  well  represented  in  the  later  Devonian.     They  were 


418 


GEOLOGICAL   STUDIES. 


mostly  Acrogens  or  Pteridophytes  of  the  classes  Ferns,  Cala- 
marians  and  Lycopods ;  though  some  Gymnosperms  were  also 
present,  especially  Cordaites,  and  possibly  also  a  few  Angio- 
sperms.  No  remains  of  Mosses  were  known  until  the  very  recent 
discovery  of  several  species  at  Commentry,  in  France.  The  stems 

are  found  three  to  four  centime- 
tres long.  Only  a  single  Fungus 
is  known  in  America,  and  that 
from  Cannelton,  Pa.  (Lesquereux). 
No  American  Palms  or  other 
Angiosperms  are  known.  The 
Ferns  were  partly  Tree  Ferns,  and 
the  whole  group  is  now  nearly 
extinct.  A  few  species  survive 
on  the  slopes  of  high  mountains 
near  the  equator  or  on  tropical 
islands  in  the  Pacific  Ocean.  A 
living  Tree  Fern  is  shown  in  Fig. 

324,  and  a  fossil  species,  restored 
by  Dawson,  is  reproduced  in  Fig. 

325.  The    "scars"    left    on    re- 
moval   of    the    leaves    of    a    Tree 
Fern  are  quite  characteristic,  and 
are  a  principal  means  of  distinc- 

j    tion  among  the  fossil  species. 

amites  restored  (after  Dawson),  with  The    greater    part    of    the    Coal 

a  spike  of  Fruit  at  summit.    327,  Sec-    Measure     ferns     were    herbaceous, 
tion  of  the  stem.    328,  The  root.    329. 

a  Fruit  Cone.   330, 1,  Aster  ophyllites.   The  commonest  species  belong  to 

332,    Annularia-tte    last    two    gen-    the       NeiirOpteriS.       PseildopeCOp- 

era   here    regarded    as    representing  . 

branches  and  leaves  of  Calamites.  teris  (Fig.  322),  bphenoptens,  and 

Pecopteris  families. 

The  Calamarians  were  related  to  the  modern  Equiseta  or 
Horsetails.  Modern  Equiseta  are  small,  herbaceous  plants,  but 
the  extinct  Calamitece  attained  a  height  of  thirty  feet.  The 
principal  genera  are  Calamites  (Figs.  326-329),  Aster  ophyllites 
(Figs.  330,  331),  Annularia  (Fig.  332),  and  ftphenophyllum. 


FORMATIONAL   GEOLOGY. 


419 


Aster ophyllites  and  Annularia,  generally  treated  as  distinct 
from  Catamites,  are  by  some  regarded  as  merely  stems  and 
leaves  of  that  genus.  More  recently  they  are  thought  to  be 
related  to  Lycopods. 


FIGS.  333-%$.— Lepidodendron.  333,  Lepidodendron  restored  (after  Dawson).  334,  335, 
Pieces  of  Bark,  showing  the  "scars."  336,  Branch  with  leaves.  337,  Leaf.  338, 
Fruit  cone.  339,  Two  scales  of  the  Fruit  cone  with  Fruit  (enlarged). 

FIGS.  340-346.— Sigillaria.  340,  Sigillaria  restored  (after  Dawson).  341,  A  Leaf.  342,  343, 
Pieces  of  Stem  of  two  different  species,  with  Bark  adhering,  showing  Scars  of  bark 
and  wood.  344,  Ideal  section  of  Stem,  showing  (a)  Pith,  (b)  Vascular  cylinder,  (c) 
Inner  layer  of  Wood,  (d)  Outer  layer  of  Wood,  (e)  Bark,  (/)  Vascular  threads  going 
from  the  vascular  layer  to  the  leaves,  and  (g)  Medullary  Rays.  345,  A  Scalariform 
vessel  from  the  inner  layer  of  wood.  346,  Perforated  vessel  from  the  outer  layer  of 
wood. 

The  class  of  Lycopods  includes  among  extinct  forms,  Lepido- 
dendron and  Sigillaria.  In  coal  production  they  hold  a  place  of 
first  importance.  Lepidodendron  was  a  genus  of  large  trees 
related  to  our  humble  ground  pines  and  Selaginella.  The  bark 
was  marked  by  scars  arranged  in  quincunx  order  as  shown  in 


420 


GEOLOGICAL    STUDIES. 


Figs.  334  and  335.  In  the  accompanying  illustrations  we  have  a 
restoration  of  Lepidodendron,  after  Dawson,  with  separate  parts 
on  a  larger  scale. 

Sigillaria  was  a  closely  related  genus  of  large  trees.  It  is 
at  once  distinguished  from  Lepidodendron  by  having  its  trunk 
scars  arranged  in  vertical  series  instead  of  diagonal.  The  parts 
of  Sigillaria  are  illustrated  in  Figs.  340-346. 

Stigmaria  (Figs. 
347,  348)  is  merely 
the  subterranean 
part  of  a  Sigillaria. 
The  types  of 
plants  thus  noticed 

have     evidently 
FIG.  W.-Stigmaria  AT  THE  BASE  OF  A  Sigillaria  STEM.        f  Qrmed  the  principal 

part  of  the  coal. 

Lepidodendron  and 
Sigillaria  sustain  rela- 
tions to  modern  Lyco- 
podium  and  Selaginella, 
but  differ  in  the  presence 

FIG.  348.  —  Stigmaria   flcoides   (so   CALLED),  WITH    of  pith;    to   CycadeCB,   in 
ROOTLETS  ATTACHED.  , ,       r ,  v    j 

the  libro-vascular  cylinder 

(Fig.  344,  #);  to  Firs,  in  their  disc-bearing,  minute  vessels  (Fig. 
346);  and  to  Ferns,  in  their  scalariform  vessels  (Fig.  345)  and 
scarred  stem  left  by  fallen  fronds  (Figs.  334,  335,  342,  and  343). 
They  are,  therefore,  striking  illustrations  of  comprehensive  types. 
They  represent  an  early  stock  existing  while  yet  there  were  nei- 
ther characteristic  Gynosperms,  Cycads,  nor  Angiosperms  ;  but 
out  of  which  all  these  types  were  to  be  gradually  unfolded. 

The  marine  life  of  the  Upper  Carboniferous  comprises  mostly 
the  family  types  descended  from  the  Devonian.  Even  most  of 
the  genera  are  the  same. 

Air-breathing  animals  now  formed  a  conspicuous  part  of  the 
fauna.  Land  Snails,  Myriapods,  and  Neuropterous  Insects,  with 
some  Orthopters,  became  comparatively  abundant.  Crustaceans 


FOKMATIONAL   GEOLOGY.  421 

increased,  but  the  type  of  Trilobites  now  made  its  last  appear- 
ance. Ganoid  and  Selachian  Fishes  continued  abundant.  The 
remains  of  Amphibians  proclaim,  like  the  other  air  breathers,  the 
increasing  importance  of  the  land.  But  they  were  mostly  scaled 
and  plated  Amphibians,  combining"  ganoid,  amphibian,  and  rep- 
tilian characters. 

7.  Origin  of  Mineral  Coal.  It  seems  to  have  been  princi- 
pally from  vegetation  which  grew  on  the  spot.  Bituminous  coals 
contain  about  81  per  cent  of  carbon,  and  anthracite  about  95  per 
cent.  The  former  contain,  in  addition,  about  5-J  per  cent  of 
hydrogen  and  12^  per  cent  of  oxygen,  and  anthracite  about  &J- 
per  cent  of  each.  Common  wood  contains  50  per  cent  of  carbon, 
6  per  cent  of  hydrogen,  and  43  per  cent  of  oxygen.  Ordinary 
coals,  therefore,  differ  from  common- woody  tissue  in  diminished 
quantities  of  hydrogen  and  oxygen:  and  this  loss  is  greatest  in 
anthracite.  This  is  the  nature  of  the  change  which  vegetable 
matter  undergoes  when  immersed  in  water. 

Next,  the  remains  of  vegetation  are  found  incorporated  in 
the  substance  of  the  coal,  and  disseminated  abundantly  through 
the  strata  associated  with  the  coal. 

Thirdly,  beds  of  peat  are  coal  beds  in  which  the  vegetable 
matter  is  still  in  the  earlier  stages  of  change,  and  are  evidently 
coal  in  process  of  formation.  But  we  know,  from  observation, 
that  peat  originates  from  plants  growing  on  or  near  the  place 
where  the  peat  accumulates. 

This  explanation  is  entirely  applicable  to  the  formation  of 
coal,  since  it  is  shown  that  vegetation  was  growing  luxuriantly  in 
the  places  where  the  coal  beds  were  forming.  The  character  of 
the  vegetation  indicates  that  it  grew  on  low  grounds;  its  preser- 
vation from  decomposition  indicates  that  standing  water  was 
generally  present,  and  the  numerous  layers  of  sandy  or  muddy 
materials  prove  that  inundations  were  of  frequent  occurrence. 
In  proportion  as  limestones  exist,  we  have  proof  of  deep  and 
lasting  inundations  by  the  waters  of  the  oceans.  The  coal- 
making  areas,  therefore,  were  little  elevated  above  standing 


422  GEOLOGICAL   STUDIES. 

water,  and  were  very  unstable  in  their  position.  They  were  sub- 
merged and  barely  emergent  in  comparatively  rapid  succession. 

The  carbon  in  the  coal  has,  therefore,  been  derived  chiefly 
from  the  atmosphere.  It  must  have  existed  there  in  the  form  of 
carbon  dioxide.  Now,  we  find  that  the  oxidation  of  a  layer  of 
carbon  2^  feet  thick  over  the  land  would  use  up  all  the  oxygen 
in  the  atmosphere.  As  the  whole  amount  of  carbonaceous  mate- 
rial in  the  earth's  crust  would  make  a  layer  of  carbon  over  three 
feet  deep,  it  appears  that  at  a  time  when  it  existed  as  carbon 
dioxide,  there  must  have  been  in  the  atmosphere  more  oxygen 
than  now  exists,  though  it  was  all  combined  with  carbon,  and 
none  existed  free  for  the  support  of  respiration.  But  the  lime- 
stones in  the  earth's  crust  represent  more  than  300  times  as  much 
carbon  dioxide  as  the  coal;  and  all  the  carbon  dioxide  of  the 
post-carboniferous  limestones  must  have  existed  in  the  atmos- 
phere along  with  that  which  yielded  the  carbon  of  the  coal. 
This,  as  calculation  shows,  was  sufficient  to  produce  a  pressure  of 
224  atmospheres.  But  a  pressure  of  80  atmospheres  renders 
carbon  dioxide  a  liquid.  It  is  evident,  therefore,  that  no  such 
amounts  of  carbon  dioxide  could  have  existed  in  the  atmosphere 
at  the  epoch  of  the  coal  measures,  or  at  any  epoch.  We  must 
conclude,  finally,  that  the  carbon  dioxide,  represented  in  the  coal 
and  the  carbonates  of  the  earth's  crust,  must  have  been  yielded 
to  the  atmosphere  progressively,  as  required.  As  there  is  no 
probability  of  its  derivation  from  the  earth,  it  seems  likely  to 
have  been  furnished  from  external  space  —  a  conclusion  of  a  very 
suggestive  character. 

8.  Growth  of  the  Land  during  the  Upper  Carboniferous 
Age.  The  configuration  of  the  land  at  the  beginning  of  the 
period  of  coal  formation  is  shown  in  Fig.  349.  It  follows  from 
what  has  been  said  of  the  progressive  northward  encroachment 
of  the  carboniferous  deposition  in  the  Illinois  basin,  and  the 
prevalence  of  the  older  coal  deposits  eastward  and  the  newer 
westward,  that  a  depression  was  in  progress  toward  the  north, 
which  brought  the  surface  progressively  to  the  low  level  requisite 
for  coal  preservation,  accompanied,  probably,  by  a  corresponding 


FORMATIONAL   GEOLOGY. 


423 


elevation  in.  southern  Illinois  and  Kentucky,  such  as  to  bring  the 
surface  too  high  for  coal-making  conditions  in  the  later  epochs 
of  the  period.  (Compare  Fig.  318.)  Correspondingly,  there  was 
a  moderate  rise  along  the  eastern  Appalachian  region  during  the 
later  epochs.  Westward,  coal-making  conditions  persisted  in 
Ohio,  Indiana,  and  Illinois,  until  the  concluding  stages  of  the 
period,  when  there  seems  to  have  been  a  recurrence  of  marine 


FIG.  349.— MAP  OF  THE  CONTINENT  NEAB  THE  BEGINNING  OF  THE  COAL  PERIOD. 

conditions  in  Illinois,  Missouri,  and  Kansas,  and  farther  west  a 
continuance  of  the  marine  conditions  which  had  existed  during 
the  Lower  Carboniferous  Age. 


424 


GEOLOGICAL   STUDIES. 


§  8.     The  Mesozoic  Great  System. 
1.    Division^  /Subdivisions,  and  Terms. 


III.     Cretaceous  System. 
Atlantic  Coast. 


2.    LATER  CRETACEOUS. 


1.  EARLIER  CRETACEOUS.  - 

II.     Jurassic  System. 

2.  FLAMING  GORGE  GROUP. 

1.  WHITE  CLIFF  GROUP. 
I.    Triassic  System. 

2.  Star  Peak  Group. 
1.   Koipato  Group. 


Interior. 

4.   LARAMIE    (LIGNIT-  "j 
ic)  GROUP.    [Also 
in  Gulf    Region. 
See  §  9.] 

3.   Fox  HILLS  GROUP,   f 

2.    COLORADO  GROUP. 
1.    DAKOTA  GROUP.      J 


ATLANTOSAURUS  BEDS. 
BAPTANODON  BEDS. 


Pacific  Coast. 
fCmco  GROUP. 


(Hiatus) 

SHASTA  GROUP. 
Horsetown  Beds. 
Knoxville  Beds. 

Jura-Trias 
or  Red  Sand- 
stone Forma- 
tion of  Atlan- 
I   tic  Coast. 


The  Triassic  System  is  so  named  from  its  threefold  division 
on  the  continent  of  Europe;  the  Jurassic,  from  the  Jura  Mount- 
ains, and  the  Cretaceous,  from  the  presence  of  great  supplies  of 
chalk.  The  Koipato  Group  commemorates  the  Indian  name  of 
the  West  Humboldt  Range,  formed  of  rocks  of  this  age.  The 
Star  Peak  Group  is  so  named  by  King  from  the  mountain  of  that 
name.  The  Group  names  for  the  Jurassic  are  derived  from 
Flaming  Gorge  on  the  Green  River  in  Wyoming,  and  the  White 
Cliffs  of  Southern  Utah  on  the  border  of  the  Grand  Canon  dis- 
trict. The  Groups  of  Interior  Cretaceous  were  named  by  Meek 
and  Hayden  from  localities  in  the  Upper  Missouri  region. 

2.  The  Triassic  System.  Triassic  rocks  are  unknown  be- 
tween the  Appalachians  and  the  eastern  slopes  of  the  Rocky 
Mountains.  In  the  eastern  province  occurs,  in  numerous  isolated 
patches,  a  formation  long  known  as  Jura-Trias,  in  consequence  of 
uncertainty  as  to  its  age.  One  of  the  principal  areas  occupies 
the  valley  of  the  Connecticut  from  New  Haven  to  the  northern 
part  of  Massachusetts.  Another  stretches  from  the  southern 
part  of  New  York  across  northern  New  Jersey,  to  the  north  of 


FORMATIONAL   GEOLOGY. 


425 


Philadelphia,  and  west  of  Washington,  into  Virginia.  Other 
smaller  areas  occur  in  western  Connecticut,  Virginia,  and  North 
and  South  Carolina.  The  rocks  are  largely  red  sandstones,  and 
in  New  Jersey  and  Connecticut  are  extensively  worked  for  build- 
ing purposes,  furnishing  the  well  known  "  brown  stones "  of 
northern  cities.  The  formation  near  Richmond,  Va.,  and  in  the 
Dan  River  and  Deep  River  districts  of  North  Carolina  embraces, 
in  the  middle  member,  valuable  beds  of  bituminous  coal.  The 
coarse  limestone  breccia  known  as  the  Potomac  Marble,  seen 
near  Point  of  Rocks,  Md.,  and  elsewhere,  lies  at  the  bottom,  and 
outcrops  along  the  western  border  of  the  principal  area.  The 
thickness  of  the  formation  rises  to  3,000  feet. 

The  eastern  Jura-Trias  has  afforded  few  organic  remains, 
except  foot  prints  and  coal  plants.  At  Portland,  and  other  local- 
ities on  the  Connecticut,  the  surfaces  of  many  of  the  layers  of 
the  brown  sandstone  are  covered  with  foot  prints  of  animals, 
many  of  which  are  believed  to  have  been  three-toed  reptiles,  such 
as  are  known  to  have  lived,  a 
little  later,  in  New  Jersey,  and 
in  other  parts  of  the  world. 
(See  page  339.)  Mammals  ap- 
peared during  this  period,  and 
a  jaw  found  in  North  Carolina 
has  been  represented  in  Fig. 
272.  The  prominent  feature  of 
the  Age  was  the  commence- 
ment of  the  great  expansion  of 
the  reptilian  type.  Fontaine 
has  recently  subjected  to  care- 
ful study  the  coal  plants  from 
this  formation,  and  found  them 
to  belong  to  the  age  of  the 
Lias;  and  it  is  quite  possible 

r.  .         FIG.  350.— SLAB  OP  SANDSTONE  PROM  TUR- 

that  the  whole  formation  is  NER'S  FALLS,  WITH  TRACKS  OP  THREE- 
Jurassic  TOED  REPTILES.  (E.  Hitchcock.)  X*V 

(a,  a,  XTV)    «,  &,  c,  Reptilian,    d,  Am- 
In    the    western    province,        phibian. 


426  GEOLOGICAL   STUDIES. 

some  beds  of  sandstones,  red  marlites,  and  gypsum  outcrop  along 
the  eastern  slope  of  the  Rocky  Mountains  (see  the  Map,  page 
119),  which  are  either  Triassic,  or  near  the  bottom  of  the  Juras- 
sic. In  the  Elk  Mountains  of  western  Colorado,  Triassic,  or 
Triassico-Jurassic  sandstones  and  marlites,  horizontally  stratified, 
make  up  a  thousand  feet  of  the  basal  portion.  Triassic  strata 
form,  also,  part  of  the  Uinta  and  Wahsatch  Mountains,  attaining 
a  thickness  of  1,000  to  1,200  feet.  In  the  West  Humboldt 
Range,  two  groups  are  recognizable.  The  lower,  or  Koipato, 
consists  of  a  great  thickness  of  quartzose  and  argillaceous  strata, 
4,000  to  6,000  feet  thick.  These,  toward  the  north,  become 
gradually  metamorphosed  into  a  porphyroid  quite  destitute  of 
stratification,  and  much  resembling  an  erupted  felsite  porphyry. 
The  upper,  or  Star  Peak  Group,  consists  of  a  vast  series  of  alter- 
nating limestones  and  quartzites,  attaining  a  thickness  of  10,000 
feet.  The  maximum  thickness  of  the  Triassic  in  the  West  Hum- 
boldt Range  is,  therefore,  about  16,000  feet.  These  two  divis- 
ions are  also  recognized  in  the  area  east  of  the  Wahsatch  Moun- 
tains; but  no  further  correlation  of  strata  can  be  shown.  Triassic 
rocks  are  also  involved  in  the  Sierra  Nevada,  and  extend  into 
eastern  California,  where  they  are  sometimes  auriferous. 

The  Koipato  Group,  which  is  represented  by  dark  red  beds 
east  of  the  Wahsatch,  is  quite  destitute  of  fossils;  while  the 
Star  Peak  Group  abounds  in  marine  forms  characteristic  of  the 
so  called  Alpine  Trias  of  Europe. 

The  Triassico-Jurassic  beds  of  the  eastern  province  rest  in 
long  northeasterly  trending  furrows  or  depressions  between 
ridges  of  Eozoic  rocks.  The  latter,  not  being  covered  by  strata 
intermediate  between  the  Eozoic  and  Trias,  appear  to  have  con- 
stituted a  part  of  the  dry  land  during  the  Palaeozoic  ages,  as 
before  mentioned,  and  as  shown  on  all  the  preceding  maps  of  the 
continent  (Figs.  297,  304,  312,  349).  After  the  Palaeozoic,  this 
region,  either  through  subsidence  or  erosion,  or  both,  became 
lowered  again  below  sea  level  in  its  eastern  part.  In  the  West 
Humboldt  basin,  similarly,  the  Trias  rests  unconformably  on  the 
eroded  Eozoic  and  Cambrian  strata.  But  in  the  Wahsatch-Uinta 


FORMATIONAL   GEOLOGY.  427 

basin,  it  rests  conformably  on  the  Upper  Carboniferous;  and  the 
succession  of  conformable  strata  is  complete  downward  to  the 
Eozoic,  showing  that  the  presence  of  the  ocean  was  there  unin- 
terrupted from  very  early  times.  [The  small  scale  of  the  Map, 
Fig.  47,  renders  it  impossible  to  represent  the  small  geological 
areas.] 

A  common  feature  of  the  Triassic  everywhere  was  the  erup- 
tion of  volcanic  materials.  The  trap  cliffs  of  Meriden,  Conn.; 
East  and  West  Rocks,  New  Haven;  the  Palisades,  on  the  Hud- 
son; Mt.  Tom  and  Mt.  Holyoke,  in  Massachusetts;  Bergen  Hill, 
in  New  Jersey;  the  ninety-mile  trap  dike  in  southeastern  Penn- 
sylvania, Fig.  313,  are  all  features  of  eruption  toward  the  close 
of  the  Triassic  Age.  Less  conspicuous  dikes  are  very  numerous. 
Similarly  erupted  products  are  intimately  associated  with  the 
Trias  of  the  far  West;  and  the  same  is  true  of  European  Trias. 

3.  The  Jurassic  System.  Except  so  far  as  indicated  in  connec- 
tion with  the  Jura-Trias  of  the  eastern  United  States,  the  Jurassic 
of  North  America  is  confined  to  the  regions  west  of  the  Missouri 
River.  The  most  easterly  beds  lie  along  the  eastern  bases  of  the 
Rocky  Mountain  ranges,  and  consist  of  reddish-yellow,  friable 
sandstones,  gray,  arenaceous  marls,  reddish-brown  bands  of  clay, 
and  thin  bands  of  cherty  limestone,  a  less  compact  dolomitic 
limestone,  and  thin  beds  of  gypsum.  These  strata  are  mostly 
destitute  of  fossils;  but  at  Como,  fossils  are  abundant,  and  fix 
the  age  of  the  formation.  The  cherty  limestone  is  quite  a  per- 
sistent horizon,  and  the  fossils  abound  in  the  marls  above  and 
below. 

In  the  Uinta  range,  in  the  Flaming  Gorge  region,  the  System, 
as  now  understood,  has  a  basal,  fossiliferous  limestone,  200  feet 
thick,  followed  by  sandstones  and  shales,  250  feet;  a  middle 
limestone,  300  feet,  with  fossils,  followed  by  clays,  shales,  and 
thin  sandstones;  and  at  the  head  of  Burnt  Fork,  a  white  sand- 
stone is  seen  at  the  top  of  the  series.  The  whole  thickness  is 
750  feet  or  over. 

In  the  Wahsatch  range  we  have  heavy-bedded  limestone  at 


428  GEOLOGICAL   STUDIES. 

the  bottom,  with  a  vast  series  of  silicious,  argillaceous,  and  calca- 
reous shales  above,  the  whole  rising  to  1,800  feet. 

In  western  Nevada,  the  limestones  in  the  lower  part  attain  a 
thickness  of  1,500  to  2,000  feet,  and  the  shales  and  slates  above, 
4,000  feet. 

Thus  the  Jurassic  strata,  which  show  a  minimum  thickness  of 
seventy-five  feet  at  the  eastern  base  of  the  Colorado  range,  grad- 
ually thicken  up  to  750  feet  in  the  Uinta,  1,800  feet  in  the  Wah- 
satch,  and  6,000  feet  in  western  Nevada.  This  is  analogous  to 
the  change  observed  in  the  Palseozoic  strata  in  passing  from  the 
Mississippi  to  the  Appalachians.  The  direction  of  the  gradation 
is  reversed;  but  the  principle  of  diminution  in  volume  with  re- 
cession from  the  source  of  the  sediments  is  the  same. 

The  slates  of  the  upper  division  of  the  Jurassic  extend  into 
eastern  California;  and  on  the  Mariposa  estate,  and  in  neighbor- 
ing regions,  become  the  gold-bearing  formation. 

On  the  southwestern  border  of  the  High  Plateaus,  near  the 
37th  parallel  and  113th  meridian,  the  Jurassic  consists  of  a  series 
of  bright-red  fossiliferous  shales,  300  to  500  feet  thick,  resting  on 
a  very  massive  bed  of  white  sandstone  nearly  a  thousand  feet 
thick. 

The  fossil  remains  of  the  Jurassic  are  characterized  by  the 
relative  abundance  of  the  Ammonite  group  of  the  Cephalopods 
(see  page  326)  ;  by  Belemnites,  or  Cephalopods  of  the  higher 
order,  Dibranchs;  by  a  great  increase  of  Lamellibranchs;  by  the 
advent  of  the  modern  crinoidal  genus  Pentacrinus,  and  an  enor- 
mous development  of  the  class  of  Reptiles  (see  page  335).  Ju- 
rassic Reptiles  of  gigantic  size  have  been  described  by  Marsh 
from  Morrison  and  Canon  City,  Colo.,  and  from  Wyoming. 

W^hile  the  Jurassic  is  unknown,  or  at  least  not  certainly  iso- 
lated, in  the  eastern  United  States,  it  is  a  widespread  formation 
through  all  the  region  between  the  Black  Hills  and  the  Sierra 
Nevada,  and  as  far  south  as  Arizona;  and,  for  its  reptilian  re- 
mains, is  a  formation  of  extraordinary  interest.  In  European 
geology  the  Jurassic  possesses  foremost  importance,  and  admits 


FORMATIOKAL   GEOLOGY.  429 

of  throe  main  divisions  —  Wealden,  Oolite,  and  Lias  —  with  sev- 
eral subdivisions  for  the  Oolite. 

4.  The  Cretaceous  System.  (1)  Distribution  and  Kinds  of 
Rocks.  The  Cretaceous  has  a  moderate  development  along  the 
Atlantic  slope,  a  larger  development  in  the  Gulf  States,  and  cov- 
ers extensive  areas  in  Texas,  and  a  still  wider  region  over  the 
Great  Plains,  along  the  eastern  slope  of  the  Rocky  Mountains. 
It  is,  besides,  extensively  involved  in  the  general  geology  of  all 
the  interior  of  the  continent,  though  extensively  overlaid  by  Ter- 
tiary strata,  as  appears  from  a  glance  at  the  Map,  Fig.  47.  On 
the  Pacific  border  it  occurs  in  the  Coast  Ranges;  and  north  of 
the  national  boundary  it  stretches  far  along  the  eastern  flanks  of 
the  Rocky  Mountains  —  perhaps  to  the  Arctic  Ocean,  and  occurs 
at  Vancouver  and  Queen  Charlotte  Islands,  and  at  many  other 
points  in  the  interior. 

In  New  Jersey  the  strata  consist,  below,  of  bluish  and  gray 
clays,  micaceous  sand  with  fossil  wood  and  angiospermous  leaves, 
130  feet,  and  above  of  dark  clays,  green  and  ferruginous  sands, 
and  yellow  limestone,  300  feet  or  over,  making  a  total  of  400  to 
500  feet.  In  Alabama  the  lowest  member,  or  "  Eutaw  Group," 
is  a  heavy  mass  of  clays,  laminated  micaceous  shales,  and  irregu- 
lar layers  of  green  sand,  with  fragments  of  dicotyledonous  leaves 
—  the  whole  over  415  feet.  Above  are  eighteen  feet  of  loose 
and  concrete  sands  with  Upper  Cretaceous  fossils,  followed  by 
the  "  rotten  limestone,"  at  least  350  feet,  uncemented  sand  45 
feet,  and  a  white,  marly  limestone,  6  feet.  Total,  about  900  feet. 

The  Cretaceous  of  the  Atlantic  and  Gulf  borders  may,  there- 
fore, be  said  to  consist  of  an  argillaceous  group  below,  and  a  cal- 
careous group  above.  The  strata  dip  gently  toward  the  Atlantic 
and  Gulf,  and  pass  under  the  Tertiary.  The  order  of  superposi- 
tion in  Alabama  is  shown  in  Fig.  351.  The  vertical  lines  show 
the  positions  of  selected  artesian  wells,  which  are  bored  in 
large  number,  into  the  lower  beds  of  the  System,  where  the 
sandy  layers  carry  supplies  of  pure,  sulphuretted  or  saline  water. 
The  Cretaceous  here  rests  directly  on  the  Coal  Measures.  The 
Permian,  Triassic,  and  Jurassic  must  underlie  in  the  region 


430 


GEOLOGICAL   STUDIES. 


Coal  Mines 
TUSCALOOSA 


Carthage 

/v/vv/y  Havana 
- — A  Bridgeville 

'Merriu-eather's  Landing 
i.  Clinton 

^/  EUTAW 

Finch's  Ferry 
Hamburg 

(CHOCTAW  BLUFF 
.1  JS'eivbern 
4=^  SELMA 
^  Pleasant  Ridge 
Bogue  Chilto  Creek 
PRAIRIK    BLUFF 


south  of  the  northern  limit 
of  the  Cretaceous.  But 
it  is  manifest  that  a  sub- 
sidence occurred  near  the 
beginning  of  the  Cretaceous, 
and  the  sea  gained  on  the 
land.  This  is  true  also  on 
the  Atlantic  border. 

The  Cretaceous  rocks  in 
Texas  consist  more  general- 
ly of  solid  limestones,  show- 
ing deeper  water  and  a  re- 
moter shore.  Tracing  the 
formation  northward,  we  find 
continued  accessions  of  ar- 
gillaceous and  fragmental 
matters.  In  the  Upper  Mis- 
souri region,  the  lowest  mem- 
ber is  the  coarse  Dakota 
Sandstone,  often  appearing 
truly  conglomeritic,  which 
comes  in  abruptly  above  the 
calcareous  beds  of  the  Ju- 
rassic. It  spreads  westward, 
southward  to  the  Uinta 
Mountains  and  Kansas,  and 
even  into  New  Mexico,  in- 
creasing in  thickness  from 
400  feet  in  Dakota  to  500  in 
the  Uintas.  Next  above  are 
the  clays  and  limestones  of 
the  Colorado  Group,  attain- 
ing a  thickness  of  1,700  feet 
on  the  Upper  Missouri,  and 
2,000  feet  in  the  Uintas. 
Then  follows  the  Fox  Hills 


EORMATIO^AL   GEOLOGY.  431 

Group  of  gray,  ferruginous,  and  yellowish  sandstones  and  are- 
naceous clays,  500  feet  thick  above  Fort  Pierre  and  along  the 
base  of  the  Big  Horn  Mountains,  and  3,000  to  4,000  feet  in 
the  Uintas.  Finally,  the  Laramie  Group,  attaining  a  thick- 
ness of  2,000  feet,  is  found  very  generally  from  New  Mexico  far 
into  British  America,  over  a  belt  500  miles  wide  and  more  than 
1,000  miles  long.  There  is  evidence  that  it  extends  southward  even 
into  Mexico.  It  consists  of  brackish-water  deposits  below,  and 
fresh-water  above.  The  rocks  are  mostly  sands,  clays,  and  shales 
colored  with  lignitic  materials,  and  containing  beds  of  bituminous 
or  semi-bituminous  coal,  known  as  lignite.  The  Laramie  contains 
plants  and  marine  shells  resembling  Tertiary  species  found  in  Eu- 
rope, and  hence  some  geologists  regard  it  belonging  to  the  Ter- 
tiary System.  But  the  Laramie  is  in  some  places  unconformable 
with  the  overlying  Tertiary  strata,  and  its  land  fauna,  containing 
Dinosaurs,  was  decidedly  Mesozoic.  Besides,  some  of  the  Mol- 
luscs possessed  Cretaceous  characters.  Dr.  C.  A.  White  has  re- 
cently shown  that  the  Chico  Group  of  California  is  probably  of 
this  age. 

(2)  Economic  Products  of  the  Cretaceous.  Cinnabar  is 
found  in  the  Coast  Ranges  of  California  in  minable  quantities. 
The  best  known  localities  are  New  Almaden,  50  miles  southwest 
of  San  Francisco,  and  New  Idria,  in  Fresno  county. 

Gold  is  found,  to  a  limited  extent,  in  the  metamorphic  Creta- 
ceous of  California,  and  so  are  copper  and  chromic  iron  ;  but 
none  of  these  are  worked.  It  may  be  here  mentioned,  that  with 
the  Carboniferous,  Triassic  and  Jurassic,  the  Cretaceous  makes 
the  fourth  system  of  strata  found  gold  bearing  in  California. 
The  age  of  the  formation,  therefore,  is  not  important.  It  is 
metamorphism  which  seems  to  have  separated  the  metal  and 
gathered  it  in  particles  and  grains  from  the  rock. 

The  Green  Sand  common  in  the  Cretaceous  of  New  Jersey 
is  mined  as  "  marl  "  for  fertilizing  purposes.  The  green  grains, 
called  also  glau'conite,  contain  8  to  12  per  cent  of  potash  and 
soda,  with  a  trace  of  phosphate  of  lime.  Some  of  the  limestones 
of  Alabama  have  recently  been  found  richly  phosphatic,  as  re- 


432  GEOLOGICAL    STUDIES. 

ported  by  Prof.  E.  A.  Smith,  and  may  prove  of  great  importance 
to  agriculture. 

Coal  is  found  to  a  considerable  extent  in  the  Dakota  Group, 
at  its  very  base,  in  the  Uinta  region.  It  occurs,  also,  on  Van- 
couver Island,  in  beds  referred  to  the  Chico  [Chee'co]  Group  of 
California,  which  is  Upper  Cretaceous  —  in  the  position  of  the 
Colorado  Group  of  the  Upper  Missouri.  In  California  coal  is 
produced  from  the  Te"jon  [Ta'-hon]  Group  in  the  Coast  Ranges, 
and  this  has  been  considered  to  hold  the  place  of  the  Lararnie 
Group  of  the  Interior;  but  Dr.  White,  in  a  recent  memoir,  has 
shown  it  to  be  of  Eocene  age.  Back  from  Se-at'tle  on  Puget 
Sound,  Washington  Territory,  coal  of  excellent  quality  is  mined. 
Ten  miles  from  Se-at'tle  is  the  so  called  Renten  coal;  at  twenty 
miles,  the  Newcastle  coal,  of  better  quality;  and  at  30  to  40  miles 
back,  on  Cedar  River,  is  the  Coleman  coal,  of  still  superior  qual- 
ity, obtained  in  a  bed  reported  40  feet  thick.  Still  farther  back, 
in  the  Foot  Hills  of  the  Cascade  Mountains,  is  said  to  occur  the 
best  of  all ;  but  this  is  not  yet  opened. 

The  coal  supplies  of  the  Cretaceous  possess  very  great  impor- 
tance, since  the  coal  is  of  good  quality,  and  is  widely  distributed 
through  regions  not  supplied  with  Palaeozoic  coal.  The  Van- 
couver and  Washington  coals  are  shipped  to  San  Francisco  and 
the  Hawaiian  Islands.  The  Laramie  Group  coal  is  widely  em- 
ployed in  Utah  at  Evanston  and  Coalville;  in  Wyoming,  at  Car- 
bon and  Hallville,  at  Black  Butte  Station  on  Bitter  Creek  and 
Bear  River,  and  in  the  Uinta  basin ;  in  Colorado,  at  Denver, 
Golden  City,  and  other  localities;  in  New  Mexico,  at  the  Old 
Placer  Mines,  in  the  San  Lazaro  Mountains.  The  bed  at  Evans- 
ton  is  26  feet  thick,  containing  37-38  per  cent  of  volatile  sub- 
stances, and  49-50  per  cent  of  carbon.  The  Wyoming  coal  is 
shipped  eastward  as  far  as  Omaha.  At  the  Old  Placer  Mines  the 
rocks  are  upturned  and  metamorphic,  as  in  eastern  Pennsylvania, 
and  the  coal,  accordingly,  is  partially  debitumenized  —  containing 
from  68  to  91  per  cent  of  fixed  carbon.  This  is  of  Laramie  age, 
and  lies  in  the  Trinidad  Coal  Field  of  Stevenson,  which  stretches 


FORMATIONAL   GEOLOGY.  433 

along  the  eastern  base  of  the  Rocky  Mountains,  lying  partly  in 
Colorado  and  partly  in  New  Mexico. 

Productive  coal  measures  occur  in  the  Cretaceous  on  the 
coasts  of  the  islands  and  main  land  north  of  Victoria,  British 
America,  at  Maple  Bar.  At  Nanaimo,  Departure  Bay,  extensive 
mines  of  Laramie  age;  also  at  Comox,  an  extensive  field  not 
worked.  Coal  partly  anthracite,  associated  with  plants  having 
Jurassico-Cretaceous  affinities,  according  to  Dawson,  has  been 
recently  reported  from  Old  Man  River,  Martin  Creek,  and  one 
other  locality  farther  northwest,  on  the  Suakwa  River.  Coal 
outcrops  are  reported  from  the  Lower  Cretaceous,  on  the  line  of 
the  Canada  Pacific  Railway,  at  the  crossing  of  the  South  Saskat- 
chewan, and  at  Bantry;  and  from  the  Laramie  at  Bassano,  Crow- 
foot, and  Coal  Creek  (long.  114°  35'). 

The  Cretaceous,  therefore,  is  a  great  coal-producing  System, 
perhaps  not  inferior  in  importance  to  the  Carboniferous.  Since 
it  produces  no  chalk  in  America,  its  name  appears  to  be  doubly  a 
misnomer. 

(3,)  Fossil  Remains  of  the  Cretaceous.  The  Brachiopods 
are  reduced  mostly  to  the  Terebratula  Family.  The  Lamelli- 
branchs  increase  in  numbers  and  diversification,  and  approach 
decidedly  toward  modern  types.  The  Oyster  family  is  largely 
developed.  Some  oysters  ( Gryphcea  mutabilis)  were  seven 
inches  in  diameter  in  Alabama,  and  other  species  (Exogyra 
costata)  were  five  inches  across;  while  Ostrea  larva  presented  a 
strikingly  falcate  form,  with  a  deeply  and  acutely  sinuate  border. 
The  Ammonite  family  continued  to  increase  in  importance  (see 
the  notice,  page  326),  but  completely  disappeared  at  the  close  of 
the  Cretaceous.  The  higher  order  of  Cephalopods,  Dibranchs, 
continued  to  increase.  The  family  of  Belemnites  was  largely 
represented.  The  Belemnite  resembled  a  modern  squid,  but  its 
internal  bone,  or  osselet,  was  prolonged  behind  in  a  cone  called 
the  pen.  This  had  a  longitudinal  cavity  (alveolus)  opening  for- 
ward, and  having  at  its  posterior  end  a  chambered  cone  called  the 
phraymocone,  which  had  a  siphuncle.  The  ink  bag  was  contained 
within  the  cavity  of  the  osselet. 


434  GEOLOGICAL   STUDIES. 

A  highly  characteristic  reptile  of  the  Cretaceous  was  the 
Mosasaurus,  described  page  338,  whose  vertebras  are  common  in 
the  Upper  Cretaceous  of  the  Gulf  region.  This  was  an  age  of 
sharks,  both  Squalodonts  and  Cestracionts.  Their  teeth  lie  scat- 
tered abundantly  over  the  exposed  Cretaceous  surfaces  of  Ala- 
bama and  Mississippi  —  by  the  roadsides,  in  the  fields,  and  along 
the  river  margins.  Teleost  fishes,  or  those  of  the  modern  type, 
became  quite  abundant.  Plants  of  modern  dicotyledonous  genera 
prevailed  in  the  forests,  besides  many  modern  forms  of  monoco- 
tyledons. On  the  whole,  the  dawn  of  the  modern  aspects  of  the 
world  was  evidently  near. 

5.  The  Physiognomy  of  the  Interior  of  tJie  Continent.  The 
Mesozoic  strata  enter  so  largely  into  the  formation  of  the  whole 
Interior  that  we  turn  for  a  moment  to  a  general  consideration  of 
its  physiognomy.  After  passing  the  "  Province  of  the  Great 
Plains,"  which  stretch  westward  from  the  Missouri  River,"  we 
reach  the  first  Ranges  of  the  Rocky  mountains  proper  —  the 
Colorado  and  Laramie  Ranges  —  the  former  also  known  as  the 
Front  Range.  These  are  succeeded  at  intervals  of  30  or  40 
miles  by  the  Medicine  Bow  and  Park  Ranges,  and  the  Sahwatch 
Mountains.  These  are  broad  massive  ranges,  serrated  with  lofty 
snow-covered  peaks,  and  trending  approximately  north  and  south. 
The  valleys  between  them  are  fertile  expanses  known  as  "  Parks," 
like  "  North,"  "  Middle,"  and  u  South  "  Parks.  Their  snows  form 
a  perennial  reservoir  for  streams  flowing,  on  one  side,  into  the 
Gulf  of  Mexico,  and,  on  the  other,  into  the  Gulf  of  California. 
These  mountains  are  sometimes  known  collectively  as  the  Park 
Mountains;  and  the  whole  zone  forms  the  "Park  Province."  It 
may  be  regarded  as  extending  to  the  107th  meridian. 

West  of  this  comes  the  "  Plateau  Province,"  a  broad  elevated 
expanse  broken  by  faults,  cut  by  gorges,  wasted  by  denudations, 
and  dotted  with  innumerable  volcanic  outbursts,  lone  mountains 
and  groups  of  mountains,  and  short  ranges.  It  is  drained  by  the 
Colorado  River  of  the  West  and  its  tributaries.  It  stands  on  an 
average  5,000  to  7,000  feet  above  the  sea.  Its  mountain  features, 
of  which  the  Uinta  constitutes  the  northern  boundary,  trend  east 


FOKMATIONAL    GEOLOGY.  435 

and  west.  Southward,  the  Plateau  Province  stretches  into  Ari^ 
zona.  It  terminates  westward  with  the  Wahsatch  Mountains,  a 
north  and  south  range  which  has  been  split  longitudinally  by  a 
great  fault,  on  the  west  of  which  the  mountain  and  the  whole 
country  has  been  sunken  six  to  seven  thousand  feet. 

The  steep  westerly  front  of  the  "Wahsatch  Range  overlooks 
the  next  province.  It  is  called  the  "  Great  Basin,"  or  "  Basin 
Province."  It  is  500  miles  wide,  stretching  to  the  Sierra  Nevada, 
and  stands  generally  at  a  level  lower  than  that  of  the  Plateau 
Province.  It  is  characterized  by  a  large  number  —  probably  over 
150  —  of  short  mountain  ranges,  which  trend  north  and  south. 
Some  of  these,  in  order  westward,  are  the  Gosiute,  Pequot,  East 
Humboldt,  Pifion,  Cortez,  Shoshoni,  West  Humboldt,  and  Monte- 
zuma  ranges.  The  Union  Pacific  Railroad  passes  the  northerly 
extremities  of  these.  On  the  south  are  numerous  other  short, 
meridional  ranges,  continuing  at  least  as  far  as  the  37th  degree 
of  latitude.  These  are  known  as  "  Basin  Ranges."  The  drain- 
age of  the  Basin  Province  is  mostly  toward  interior  salt  lakes. 

The  Basin  Province  is  bounded  by  the  Sierra  Nevada,  another 
great  mountain  range  split  longitudinally  along  its  crest,  with 
the  eastern  half  let  down  3,000  to  10,000  feet.  The  steep  east- 
ern face  of  the  Sierra  Nevada  overlooks  the  Great  Basin  toward 
the  east,  as  the  Wahsatch  faces  it  toward  the  west.  From  the 
summit  of  the  Sierra  Nevada  the  country  slopes  generally  toward 
the  Pacific,  and  forms  the  "  Pacific  Province."  The  Coast  Ranges 
of  California,  however,  interrupt  the  slope,  and  cause  a  longitu- 
dinal valley  along  the  centre  of  the  state,  stretching  from  Mt. 
Shasta,  on  the  north,  to  far  beyond  Tulare  Lake  on  the  south. 
From  the  north  along  this  valley  flows  the  Sacramento  River;  and 
from  the  south  the  San  Joaquin.  The  two  bend  westward  on  the 
38th  parallel,  and  find  exit  through  the  Coast  Ranges  into  the 
Bay  of  San  Francisco. 

The  name  Rocky  Mountains  is  by  some  employed  to  embrace 
all  the  mountains  from  the  Colorado  Range  to  the  Sierra  Nevada. 
But  this  seems  objectionable.  The  breadth  of  country  is  more 
than  a  thousand  miles.  The  mountain  features  are  not  conform- 


436  GEOLOGICAL   STUDIES. 

able  to  one  plan;  they  do  not  constitute  one  system;  they  were 
uplifted  at  various  geologic  epochs;  they  are  separated  by  broad 
intervals  ;  they  are  formed  of  rocks  of  various  ages.  We  may 
designate  as  Cordilleras,  after  Humboldt,  the  entire  assemblage 
of  mountains,  and  restrict  the  name  "  Rocky  Mountains  "  to  the 
Park  Ranges  along  the  eastern  border.  These  constitute  the 
dividing  ridge  between  the  waters  flowing  into  the  Mississippi 
and  those  flowing  into  the  Pacific. 

6.  Comparative  Geology  of  the  Provinces.  The  central 
masses  of  the  Park  Mountains  are  of  Eozoic  strata,  and  are  en- 
wrapped, often  unconformably,  by  Palaeozoic  formations.  All 
these  are  involved  in  the  disturbances  of  the  primitive  upheavals. 
Mesozoic  and  Caenozoic  formations  abut  against  the  uplifted  slopes, 
and  have  been  themselves  tilted  by  later  upheavals,  and  extensively 
wasted  by  denudation.  (See  the  section,  Fig.  352.)  The  old  nuclei 
were  extensively  plicated  with  closely  appressed  folds  prior  to 
the  deposition  of  the  later  sediments.  The  Park  Mountains 
stood  as  long  islands  in  the  midst  of  the  ocean  of  Mesozoic  and 
Casnozoic  times.  This  stretched  from  beyond  the  Wahsatch 
Mountains  eastward.  It  covered  the  whole  of  the  Plateau  Prov- 
ince till  late  in  Caenozoic  time,  and  continued  to  receive  the  sedi- 
ments contributed  from  the  ancient  continent  farther  west.  The 
Plateau  Province  is  almost  wholly  underlaid  by  post-Palaeozoic 
strata,  though  in  places  upheaval  and  erosion  bring  Carboniferous 
strata  into  view.  The  Basin  Province,  now  so  depressed,  was, 
till  Caenozoic  time,  the  most  elevated  region  of  the  Interior.  It 
is  underlaid  by  Eozoic  and  Palaeozoic  rocks,  with  some  Meso- 
zoic and  Caenozoic  in  the  Humboldt  Mountain  district.  It  was 
mostly,  during  Mesozoic  and  Caenozoic  time,  a  continental  mass, 
with  drainage  eastward  into  the  ocean  of  the  Plateau  Province. 
It  supplied  the  sediments  which  overspread  its  bottom,  and 
was  wasted  by  the  service.  Finally,  in  late  Tertiary  time,  the 
Plateau  region  was  raised  above  the  level  of  this  ancient  land, 
and  the  Park  region  was  elevated  still  higher.  Thus  the  direc- 
tion of  the  drainage  was  reversed. 

The  uplift  of  the  Great  Plateau  was  accompanied  by  an  ex- 


FORMATIOtfAL   GEOLOGY. 


437 


tensive  system  of  faults,  which  rent  the  Plateau 
Province  from  north  to  south.  The  huge  result- 
ing prismoids  present  the  various  attitudes  and 
mutual  relations  which  have  been  described  as 
Kaibab  structure,  Uinta  structure,  and  mono- 
clines (page  160).  These  features  are  illustrated 
in  Figs.  85,  86,  and  87.  Volcanic  outflows  have 
contributed  to  further  modify  the  surface,  form- 
ing sometimes  mountain  saliences  above  the  pla- 
teau, and  sometimes  broad  sheets  on  which 
erosion  has  subsequently  acted,  cutting  slit-like 
gorges  and  carving  high  mesas,  which  rise  like 
titanic  tables  here  and  there  over  the  scarred  and 
desert  expanse.  Some  of  the  most  important  vol- 
canic mountains  in  this  Province  are  Pilot  Butte, 
the  Uinkarets,  and  San  Francisco  Mountain.  Here 
also  are  the  mountains  of  the  laccolitic  type,  like 
the  Henry,  the  Navajo,  and  Sierra  la  Sal  (see 
page  157).  In  southern  Utah  the  Csenozoic  and 
Mesozoic  formations  terminate  in  a  succession  of 
gigantic  steps  descending  toward  the  Colorado 
River,  whose  "  Grand  Canon "  cuts  five  and  six 
thousand  feet  deeper  into  Palaeozoic  and  Eozoic 
rocks.  The  canon  features  are  illustrated  in  Fig. 
31;  and  a  bird's-eye  view  of  the  southern  part  of 
the  Plateau  Province  is  shown  in  Fig.  87. 

7.  Geological  History  of  the  Cordilleran  Re- 
gion. It  will  be  remembered  that  the  Cordilleran 
wing  of  the  continent  at  the  end  of  Eozoic  time 
stretched  in  width  from  the  Nevada  region  east- 
ward to  the  104th  meridian;  and  that  it  then  be- 
gan to  sink,  and  continued  sinking  during  the 
entire  progress  of  Palaeozoic  time,  so  that  finally 
only  the  highest  peaks  rose  through  the  mantle 
of  sediments.  The  Cordilleran  ocean  was  now, 
as  it  had  long  been,  an  archipelago;  and  the  vast 


•i 


438  GEOLOGICAL  STUDIES. 

series  of  Palaeozoic  sediments,  covering  the  ancient  continent 
unconformably,  were  entirely  conformable  among  themselves 
—  a  state  of  things  quite  unlike  the  frequently  occurring  un- 
conformabilities  east  of  the  Mississippi. 

Widespread  mechanical  disturbances  now  occurred.  The  land 
area  west  of  the  Nevada  Palaeozoic  shore  became  depressed,  while 
all  the  thickest  part  of  the  Palaeozoic  deposits  from  the  Nevada 
shore,  eastward  to  and  including  the  Wahsatch,  rose  above  the 
ocean  and  became  a  land  area  (King).  Between  the  new  conti- 
nent and  the  old  one  which  went  down,  to  the  west,  there  was  a 
complete  change  of  condition.  The  land  became  ocean,  the 
ocean  became  land.  The  new  land  extended  eastward  to  include 
the  Wahsatch.  Eastward  of  that,  to  the  Great  Plains,  and  in- 
cluding them,  the  former  ocean  bed  remained  undisturbed.  The 
new-made  land,  from  the  Wahsatch  to  117°  30'  west,  now  yielded 
the  sediments  destined  to  form  all  the  post-Carboniferous  forma- 
tions. That  is,  the  Basin  Province  was  then  the  continent,  and 
eastward  stretched  a  vast  mediterranean  sea,  as  far  as  Kansas  and 
Nebraska,  and  southward  to  the  Gulf  of  Mexico,  and  northward 
probably  to  the  Arctic  Ocean.  (Compare  the  map  of  America  at 
this  epoch,  Fig.  353.)  W^est  of  the  new  land  mass  of  the  Basin 
Province,  the  successive  deposits  of  the  Triassic  and  Jurassic  Ages 
were  laid  down  in  conformable  sheets  of  enormous  thickness,  di- 
rectly but  unconformably  upon  the  ancient  Eozoic  floor.  East  of 
the  same  land  mass,  the  Triassic  and  Jurassic  sediments  rested  con- 
formably on  the  top  of  the  Carboniferous.  West  of  the  Basin- 
Province  Land,  over  the  Sierra  Nevada  belt  and  California,  the 
Mesozoic  sediments  attained  a  thickness,  by  the  close  of  Jurassic 
time,  of  20,000  feet ;  in  the  mediterranean  sea,  a  thickness  of 
only  3,800  feet.  The  western  sea  was  deep;  the  mediterranean 
was  shallow. 

At  the  close  of  the  Jurassic  Age,  the  western  ocean,  with  its 
original  floor  of  Eozoic  ranges,  overlaid  by  twenty  odd  thousand 
feet  of  Jura-Trias  sediments,  suffered  abrupt  orographical  uplift, 
resulting  in  the  sharply  folded  ranges  of  the  Sierra  Nevada,  and 
extending  the  continent  200  miles  further  west.  This  uplift 


FORMATIOKAL   GEOLOGY. 


439 


stretched  south waid  as  far  as  the  36th  parallel,  and  northward 
probably  to  Alaska.  East  of  the  Wahsatch,  however,  everything 
remained  undisturbed.  The  earliest  sediments  of  the  Cretaceous 
were  laid  down  conformably  over  the  Jurassic.  But  the  great 
event  which  had  marked  the  history  of  the  Basin  and  Nevada 
provinces  was  signalized  over  the  Plateau  and  Park  provinces  by 
an  invasion  of  coarse  and  even  conglomeritic  deposits.  These 
constitute  the  Dakotah  Group  of  the  Cretaceous.  They  stretch 


FIG.  353.  —  NORTH  AMERICA,  NEAR  THE  BEGINNING  OP  THE  MESOZOIC 


from  the  Wahsatch  into  Kansas.  They  covered  the  entire  bottom 
of  the  mediterranean  sea;  that  is,  the  entire  Province,  with  the 
exception  of  a  few  Eozoic  islands  which,  from  the  time  of  the 
Cambrian,  had  stood  above  the  plane  of  deposition.  This  phy- 
sical condition  of  things  continued  through  the  Cretaceous.  The 
greatest  thickness  attained  by  deposits  of  this  Age  was  along  the 
western  border  of  the  ocean,  where  we  find  about  12,000  feet  of 
Cretaceous.  Passing  eastward,  the  thickness  diminishes.  Along 
the  eastern  base  of  the  Rocky  Mountains,  we  find  it  thinned  to 


440 


GEOLOGICAL   STUDIES. 


4,500  or  5,000  feet;  while  in  western  Kansas  its  development  is 
at  a  minimum. 

While  the  Jura  deposits  had  been  generally  fine  and  argillo- 
calcareous,  those  of  the  Cretaceous  began  abruptly  in  a  coarse, 
silicious  conglomerate.  Along  the  borders  of  the  Wahsatch  we 
find  many  of  the  pebbles  a  foot  in  diameter.  Farther  east,  they 
continually  diminish,  and  in  Kansas  no  pebbles  are  to  be  seen. 
In  the  region  of  the  Wahsatch  and  Uinta  ranges,  coal  beds 


FIG.  354.— NORTH  AMERICA,  NEAR  THE  BEGINNING  or  THE  CRETACEOUS  AGE. 

appear  at  the  very  base  of  the  series,  immediately  upon  the  Jura; 
and  they  continue  to  recur  at  intervals  through  the  whole  thick- 
ness of  the  Cretaceous.  They  increase  in  frequency  after  the 
close  of  the  Fox  Hill  Group,  and  make  their  appearance,  also,  in 
the  province  of  the  Great  Plains.  Finally,  through  the  4,000  or 
5,000  feet  of  the  Laramie  Group,  the  coal  becomes,  over  the 
whole  Cretaceous  area,  abundant  and  characteristic.  The  western 
part  of  the  Cretaceous  repeats,  therefore,  the  geological  history 
of  the  Carboniferous  Coal  Measures,  in  a  region  where  those 


FORMATIONAL    GEOLOGY.  441 

measures  have  no  existence.  We  infer  that  the  water  began  to 
shallow  early  in  the  Cretaceous,  and  that  the  shallowing  extended 
eastward  during  the  progress  of  that  Age. 

The  Cretaceous  ends  the  long  series  of  conformable  deposits 
over  the  Plateau  Province,  continuing  from  the  Cambrian  onward. 
Its  close  was  marked  by  an  upward  and  undulatory  movement, 
which  was  felt  from  the  eastern  base  of  the  Rocky  Mountains  to 
the  eastern  base  of  the  Wahsatch.  The  Uinta,  with  its  broad, 
flat  anticlinal  (Fig.  82),  now  arose.  The  whole  chain  of  the 
Rocky  Mountains  was  further  uplifted,  and  the  broad,  shallow 
basin  of  the  Colorado  was  defined.  On  the  Pacific  coast,  this 
disturbance  was  not  felt,  though  there  are  indications  that  the 
region  of  the  Cascade  Range  was  now  marked  out.  The  most 
important  result  of  this  post-Cretaceous  movement  was  the  eleva- 
tion of  the  whole  interior  of  the  continent,  and  the  complete 
extinction  of  the  inter- American  mediterranean  ocean.  The  land 
of  the  western  limb  of  the  continent  was  now  joined  to  the  land 
of  the  eastern  limb,  and  the  destined  completion  of  the  continent 
was  distinctly  foreshadowed. 

The  Csenozoic  history  of  the  Cordilleran  region  will  be  given 
in  its  proper  connection. 

§  9.     The  Csenozoic  Great  System. 
1.  Divisions,  Subdivisions,  and  Terms. 

II.  Q-uater'nary  System. 
3.  RECENT,  or  TERRACE  FORMATION. 

2.  CHAMPLAIN  FORMATION.    Fresh  water  Erie  Clays  (Logan).    Marine  Leda  Clays 

(Dawson). 

1.  GLACIAL,  or  DRIFT  FORMATION. 
(3)  Second  Glacial  Deposits. 
(2)  Interglacial  Deposits. 

(1)  First  Glacial  Deposits. 
I.  Tertiary  System. 

3.  PLIOCENE  GROUP,  -) 

(2)  Equus  Beds  (Postpliocene?)  of  Pacific  slope, 

i  Procamelus  Beds  (Cope),       SUMTER 

(1)  Loup  River  Beds,  \  Ticholeptus  Beds  (Cope),    \  GROUP, 

=  Niobrara,  Marsh  and  King, 


-j-Humboldt,  King  +  North  Park  (Hayden and  Hague),         J 
2.  MIOCENE  GROUP, 
(2)  Truckee  Formation  (in  the  West), 

(  =  John  Day  Group,  King),  contemporary  with    \.  YORKTOWN   GROUP, 
(1)  White  River  Formation    (on  Great  Plains), 


NEOCENE. 


442  GEOLOGICAL   STUDIES. 


1.  EOCENE  GROUP,  1  f  Vicksburg,  175?  ft.,  i  W  h  i  t  e  L  i  m  e  - 

V    stone  (Oli go- 
Jackson,  60  ft.,          ]     cene). 


(4)  Uinta  Formation, 

(= Brown's  Creek,  Powell), 
(3)  Bridger  Formation, 
(2)  Wahsatch  Formation,          |   ALABAMA  H 
(  =  Vermillion  Creek,  King,    J-     nvMro 

or  Bitter  Creek,  Powell), 
(6)  Green  River  Division, 
(?=Elko  Group,  King), 


GROUP, 


"I  O  f  Calca- 
Claiborne,  150  ft.,       |  g.  |   reous, 


Buhrstone,  175-200,  |  §    |     Sili-    I 
t  cious,  j 


(a)  Wahsatch  Division, 
(1)  Puerco  Formation  of  Cope,  J  The  Tejon  Group,  California,  is  Eocene. 

f  Bluff  Lignite,  1  o  o 

Lignitic,  1,000  ft.,  -j  Orange  Sand,  or  La  Grange,  [  g  » 

|_  Porter's  Creek,  j  *  T 

The  terms,  "Tertiary  and  "Quaternary"  are  survivals  of 
an  old  system  of  nomenclature  in  which  "  Secondary  "  was  nearly 
equivalent  to  our  "  Mesozoic,"  and  "  Primary  "  had  a  somewhat 
undefined  range  over  rocks  older  than  "  Secondary."  "  Eocene," 
"Miocene,"  and  "Pliocene,"  introduced  by  Lyell,  are  from  Greek 
terms,  signifying  "  Dawn  of  the  Recent,"  "  Less  Recent,"  and 
"More  Recent."  Some  include  the  upper  part  of  the  Eocene, 
and  the  lower  of  the  Miocene,  in  another  group,  "  Oligocene," 
which  signifies  "slightly  recent."  The  Miocene  and  Pliocene, 
taken  together,  are  sometimes  designated  "  Neocene,"  signifying 
"newer  recent."  The  subdivisions  of  the  Tertiary  groups  are 
designated  by  geographical  terms.  Those  most  distinctly  limited 
belong  to  the  Great  Plains  and  the  Cordilleran  region.  The 
Puerco,  though  generally  regarded  as  embraced  in  the  Wahsatch, 
is  urged  by  Cope,  with  good  reasons,  as  a  coordinate  group  below 
the  Wahsatch.  The  terms  employed  for  the  divisions  of  the 
Quaternary  refer  to  the  physical  conditions  prevailing  —  except 
"  Champlain,"  which  alludes  to  the  basin  of  the  lake  of  that 
name. 

2.  Geographical  Distribution  of  the  Tertiary.  The  Tertiary 
strata  accessible  to  study  embrace  only  the  limited  areas  which 
have  been  raised  above  water  level,  or  otherwise  drained,  since 
the  close  of  Mesozoic  time.  They  are,  therefore,  of  comparatively 
small  extent,  and  partly  in  detached  interior  regions.  A  belt  of 
marine  Tertiary  strata  extends  from  Martha's  Vineyard  over 
Long  Island,  southern  New  Jersey  and  the  Atlantic  coast  to  Key 


FORMATIONAL   GEOLOGY. 


443 


West,  and  thence  around  the  Gulf  border  into  Mexico.  It  grad- 
ually increases  in  width  to  Florida,  attaining  in  Georgia  a  breadth 
of  245  miles.  In  the  valley  of  the  Mississippi  it  spreads  out  in  a 
deltoid  form,  reaching,  with  its  apex,  to  the  mouth  of  the  Ohio. 
A  belt  of  marine  Tertiary  stretches  along  the  Pacific  coast,  form- 
ing, with  the  Cretaceous,  the  Coast  Ranges  of  mountains.  Sev- 
eral detached  but  extensive  areas  of  fresh-water  Tertiary  occur 
in  the  Interior.  The  Great  Plains,  up  to  the  bases  of  the  Rocky 
Mountains,  and  southward  to  the  Gulf  of  Mexico,  are  covered 
with  lacustrine  Tertiary,  chiefly  of  Pliocene  age,  at  surface. 
Another  Pliocene  basin  exists  in  Nevada,  and  a  third  in  the  North 
Park.  A  great  basin  stretching  from  the  Colorado,  or  Front 
Range  westward  to  the  Wahsatch  is  of  Eozene  age.  Northwest 
it  extends  to  the  Wind  River  Mountains,  over  the  so  called  Green 
River  Basin,  and  southward  it  stretches  into  New  Mexico.  Over 
part  of  the  eastern  slope  of  the  Rocky  Mountains,  along  the 
valley  of  the  White  River,  are  Tertiary  deposits  of  Miocene  age, 
underlying  the  Pliocene;  and  others  spread  through  central  Ore- 
gon along  the  John  Day  River.  The  Eocene  beds  of  the  Cordil- 
leran  region  attain  a  thickness  of  10,000  feet.  The  Puerco  of 
Cope,  which  perhaps  is  not  included  in  the  estimate,  extends 
from  the  sources  of  the  Puerco  River  in  New  Mexico,  northward 
and  a  little  east  of  the  Wahsatch  Mountains,  consisting  of  green 
and  gray  marls,  500  to 
1,200  feet  thick.  Coryph'- 
odon  and  other  mam- 
mals of  the  Wahsatch 
group  are  wanting;  but 
Marsh  subordinates  the 
Puerco  to  the  Wahsatch. 
The  Tertiary  strata 
are  generally  little  cohe- 
rent. They  have  conse- 
quently been  worn  by 
rains  into  deep  ravines, 
and  fluted  slopes,  and  isolated  columns. 


FIG.  355.— VIEW  IN  THE  BAD  LANDS  OP  NEW 

MEXICO.    (Cope.) 


Such  areas  being  desti- 


444  GEOLOGICAL   STUDIES. 

tute  of  verdure  and  soil,  are  known  as  mauvaises  terres,  or  "bad 
lands" — a  designation  first  applied  to  a  portion  of  the  White 
River  region.  A  view  in  one  of  these  Bad  Lands  in  New  Mexico 
is  given  in  Fig.  355. 

3.  Organic  Remains  of  the  Tertiary.     The  three  great  divis- 
ions of  the  Tertiary  are  based  on  the  percentage  of  molluscan  spe- 
cies belonging  to  the  recent  fauna.     In  the  Eocene  the  percentage 
of  recent  species  is  small;  in  the  Miocene,  less  than  half,  and  in  the 
Pliocene,  more  than  half.     Generally,  however,  the  aspect  of  the 
molluscan  fauna  was  decidedly  modern.     It  contained  few  Bra- 
chiopods,    numerous    Lamellibranchs    and    Gasteropods,   and    no 
chambered  shells  except  Nautilus.      Sharks    of    the   Squalodont 
type  were  very   abundant;    and  Teleost  Fishes  prevailed   as   in 
modern  seas.     The  remains  of  the  latter  are  of    very  frequent 
occurrence  in  the  Green  River  Shales,  in  the  upper  part  of  the 
Wahsatch  formation. 

The  great  feature  of  the  organic  life  of  the  Tertiary,  how- 
ever, was  its  Mammals.  Dugongs  and  Whales  abounded  in  the 
sea.  Zeuglodon,  a  whale-like  mammal  with  an  attenuated  pos- 
terior part,  attaining  a  length  of  over  70  feet,  has  left  its  bones 
in  the  White  Limestone  of  the  Eocene  of  the  Gulf  States.  Ver- 
tebras of  whales  are  found  at  Gay  Head  on  Martha's  Vineyard, 
together  with  the  teeth  of  Squaloids. 

The  land  Mammals,  which  were  far  more  important,  have 
been  already  noticed  as  far  as  space  permits  on  pages  348-358, 
which  the  student  should  now  review. 

4.  Quaternary    Materials.      Here    we    return    to    the    point 
from  which  we  started  on  entrance  upon   this  study.      In  Part  I, 
Studies  I-III,  attention  was  directed  to  the  materials  of  the  Drift, 
and  their  method  of  arrangement.      These  Studies  should  be  now 
reviewed.      The  principal  object  of  the  next  eleven  Studies  (IV- 
XIV)  was  to  become  acquainted  with  the  materials  of  the  Drift. 
In  Studies  XV  and  XVI  we  also  considered  phenomena  of  the 
Drift.     Thus  the  simple  observation  of   things  nearest  at  hand 
led  our  thoughts  to  operations  performed  many  ages  before  man 
existed  on  the  earth  —  operations  of  erosion  and  sedimentation 


FORMATIOKAL   GEOLOGY.  445 

which  have  contributed  so  greatly  to  form  the  vast  rock  masses, 
and  sculpture  the  terrestrial  surface  into  the  forms  which  it  pre- 
sents to  our  eyes.  In  this  place,  therefore,  we  have  only  to  refer 
to  what  has  been  said,  and  add  a  few  statements  of  facts  not  so 
easily  observed. 

(1)  Phenomena  of  the  Surface  Materials.  A  line  having  a 
general  westerly  direction  from  Sandy  Hook  through  Cincinnati 
marks  the  southern  limit  of  bowlders.  From  Cincinnati  it  con- 
tinues to  the  parallel  of  38°  in  southern  Illinois  and  Missouri; 
but  west  of  the  Missouri  River  it  trends  in  a  direction  parallel 
with  the  river  into  Dakota.  The  incoherent  surface  materials  on 
the  south  of  this  line  differ  in  several  respects  from  such  materials 
on  the  north  of  it.  (a)  On  the  south  there  are  drifted  materials, 
as  well  as  on  the  north,  but  bowlders  larger  than  pebbles  are 
wanting.  (b)  On  the  north  we  notice  a  distinction  of  unstratified 
Drift,  semi-stratified  Drift,  and  stratified  Drift.  The  first  consists 
of  clay  with  imbedded  bowlders,  lying  generally  on  the  bed  rock, 
but  often  outcropping  at  the  surface.  The  second  consists  of 
sand,  clay,  pebbles,  and  a  few  larger  bowlders,  showing  oblique 
and  irregular  lamination,  and  holding  position  above  the  till  or 
unstratified  Drift.  This  has  evidently  been  moved  and  laid  down 
by  powerful  and  irregular  currents  of  water.  The  stratified 
Drift  is  composed  of  horizontal  beds  of  fine  materials,  mostly 
along  the  borders  of  lakes,  or  in  situations  from  which  lakes 
have  disappeared.  It  appears  to  be  the  result  of  lacustrine  action, 
and  is  thus  a  "lacustrine  formation."  Its  position  is  above  the 
semi-stratified  Drift.  Another  form  of  obscurely  stratified  mate- 
rials occurs  sometimes  along  river  valleys.  It  is  fine,  loamy,  buf- 
fish,  and  calcareous,  with  occasional  remains  of  vegetation  and 
land  animals.  It  is  known  as  loss,  a  German  term.  It  may  be 
seen  on  the  Mississippi  River  at  Vicksburg,  Memphis,  and  Daven- 
port; on  the  Des  Moines  at  Des  Moines,  and  on  the  Missouri  at 
Council  Bluffs  and  Omaha.  We  find,  also,  fluviatile  deposits  of 
recent  origin.  The  term  Drift,  as  ordinarily  employed,  is  not 
understood  to  embrace  the  lacustrine,  loss,  and  fluviatile  depos- 
its, though  they  are  all  mostly  modifications  of  Drift.  On  the 


446  GEOLOGICAL   STUDIES. 

south  of  the  boundary  line  named,  the  unstratified  Drift  is  want- 
ing; but  semi-stratified  Drift  is  generally  present,  together  with 
occasional  lacustrine,  and  more  abundant  fluviatile  and  loss 
deposits. 

(c)  On  the  north  of  the  boundary  line  the  Drift  materials 
extend  downward  to  the  bed  rock,  and  end  abruptly  on  a  solid, 
but  sometimes  shattered,  rock  surface.  The  solid  surface  is  gen- 
erally smoothed  and  marked  by  grooves  and  stride.  On  the  south, 
the  obliquely  laminated  Drift  near  the  surface  mingles  gradually 
with  materials  resulting  from  the  disintegration  of  the  rock  im- 
mediately underlying,  until  the  latter  materials  predominate; 
traces  of  the  original  stratification  appear;  the  substance  grows 
less  and  less  changed,  and  passes  downward  by  degrees  into 
sound,  unaltered  bed  rock.  That  is,  in  the  south  the  lower  part 
of  the  surface  deposits  seems  to  have  resulted  from  the  decay  of 
the  underlying  strata,  and  we  can  trace  the  stratification  upward 
from  the  unaltered  rock  into  the  overlying,  unconsolidated  beds. 
These  lower  portions  have  been  formed  where  they  lie;  only  the 
higher,  gravelly  portions  have  been  brought  from  some  other 
region.  The  lower  portions,  therefore,  are  not  properly  any  part 
of  the  Drift.  The  upper,  transported  sand  and  gravel  are  much 
less  abundant  than  the  proper  Drift  of  the  North;  but  yet,  in 
some  localities,  they  are  found  one  or  two  hundred  feet  thick. 

(2)  Relation  of  Drift  Phenomena  to  Climatic  Causes.  It 
thus  appears  that  the  geological  action  which  in  the  north  re- 
moved the  decayed  rock,  smoothed  and  striated  the  general  rock 
surface,  and  distributed  the  bowlders,  ceased  to  operate  in  about 
the  latitude  of  Cincinnati.  It  was  an  action  correlated  to  climate, 
since  the  differences  are  latitudinal,  and  the  separating  line,  in 
mountain  regions,  is  deflected  southward,  like  an  isotherm. 

The  smooth  and  striated  condition  of  the  bed  rocks  throughout 
the  northern  states  (see  Figs.  200  and  213)  is  a  condition  such  as 
is  produced  in  modern  times  in  all  glacier-covered  regions  (pages 
280-284);  the  transportation  of  bowlders  is  a  phenomenon  of 
glacier  action ;  and  thus  the  two  most  characteristic  features  of 
the  Drift  are  traceable,  not  only  to  climatic,  but  to  glacial  causes. 


FORMATIOXAL   GEOLOGY.  447 

Again,  the  deposition  of  the  semi-stratified  Drift  appears  to  have 
resulted  from  some  torrential  action,  such  as  might  be  caused  by 
the  rapid  conversion  of  ice  into  water.  Thus,  while  striae  and 
bowlders  are  phenomena  which  suggest  a  geological  winter,  mod- 
ified Drift  is  a  phenomenon  suggesting  a  geological  springtime. 
Comparing  the  North  and  South,  we  see  that  the  ice  of  the  geo- 
logical winter  did  not  pass  the  parallel  of  39°;  the  floods  of  the 
geological  springtime  rushed  to  the  Gulf  of  Mexico. 

(3)  More  Critical  Observation  of  the  Drift.  Now  that  we 
plainly  see  reasons  to  regard  the  Drift  as  the  result  of  glacier 
action,  much  light  is  shed  on  the  nature  of  other  phenomena. 
The  broad  sheet  of  commingled  clay,  sand,  gravel,  and  bowlders 
firmly  compacted  together,  lying  immediately  on  the  rock  floor, 
may  be  regarded  as  Subglacial  Till  laid  down  beneath  the  thin- 
ning marginal  portion  of  the  ice  sheet.  The  sheet  in  some  places 
overlying  this,  similar  in  character,  but  less  compact,  is  Englacial 
or  Superglacial  Till,  formed  of  materials  imbedded  in  the  ice,  or 
accumulated  on  its  surface;  while  the  more  homogeneous  till,  with 
occasional  traces  of  stratification,  and  holding  a  higher  position, 
is  Subaqueous  or  Floe  Tilly  formed  under  water  through  the 
agency  of  floating  ice.  (Chamberlin.) 

In  the  modified  Drift  we  make  (following  Chamberlin)  the 
following  discriminations:  The  long  narrow,  sharp  ridges  of 
gravel  and  sand,  with  some  bowlders,  stretching  out  from  higher 
to  lower  levels,  and  following  generally  the  courses  of  the  larger 
valleys,  are  Osars.  The  assemblages  of  conical  hills  and  short, 
irregular  ridges,  with  intervening  depressions  and  bowl-shaped 
hollows,  are  I£ames  (Fig.  5).  Unlike  the  osars,  they  tend  rather 
to  stand  transverse  to  the  slope  of  the  surface,  and  to  the  direc- 
tion of  the  glacier  movement. 

Among  phenomena  connected  with  glacier  action,  we  dis- 
criminate lateral,  median,  interlobate,  and  terminal  moraines. 
Lateral  moraines  are  accumulated  along  the  borders  of  a  glacier 
(Fig.  211);  median  result  from  the  union  of  two  contiguous 
lateral  moraines,  where  two  glaciers  become  confluent;  interlo- 
bate  moraines  result  from  the  joint  action  of  two  adjacent  glacier 


448  GEOLOGICAL   STUDIES. 

lobes  or  tongues,  which  push  their  contiguous  lateral  moraines 
together  without  becoming  properly  one  glacier  stream.  A  ter- 
minal moraine  accumulates  in  front  of  the  glacier,  so  that  when 
the  glacier  retreats,  the  moraine  remains  as  a  curved  ridge  of 
confused  or  locally  stratified  materials.  (See  Figs.  211,  212.) 

(4)  The  Terminal  Moraine  of  the  Ancient  Glacier.  The 
continental  glacier  of  the  United  States  must  not  be  conceived 
as  one  continuous  sheet  of  ice,  moving  forward  with  equal  pace 
in  all  its  parts,  and  accumulating  a  rigidly  continuous  moraine, 
stretching  along  an  unbroken  glacier  front.  The  great  glacier 
suited  itself  to  the  topographical  configuration  of  the  land.  It 
must  be  viewed  as  a  viscid  fluid  pursuing  the  courses  of  the  great 
valleys,  and  protruding  its  front  in  irregular  lobes,  in  varying 
directions  and  to  varying  distances,  according  to  the  direction 
and  length  of  the  valley  axes.  On  the  general  retreat  of  the 
great  glacier,  therefore,  the  continental  moraine  would  consist  of 
a  series  of  crescentic  ridges  more  or  less  disconnected.  So  we 
find  it. 

But  we  must  now  remark  that  the  glacial  period  in  North 
America,  as  in  Europe,  appears  to  have  been  divided  into  two  or 
more  epochs,  separated  by  one  or  more  interglacial  epochs.  Evi- 
dences of  such  division  have  been  detected  in  so  called  "dirt 
beds"  in  Illinois  and  elsewhere,  intercalated  in  the  glacial  Drift. 
.Indications  of  similar  purport  are  found  in  New  Jersey.  We 
have,  accordingly,  the  phenomena  of  two  or  more  glacier  termi- 
nations. The  older  epoch  was  marked  by  a  glacier  which  had  for 
its  southern  limit  the  line  which  has  already  been  traced,  and 
which  is  shown  in  detail  in  Fig.  356.  The  newer  epoch  appears 
to  have  been  marked  by  a  glacier  leaving,  generally,  a  more 
northern  moraine.  Both  moraines  have  recently  been  traced 
across  the  whole  extent  of  the  country  from  Cape  Cod  to  Dakota. 
For  this  work  we  are  indebted  chiefly  to  Messrs.  Lewis  and 
Wright  for  the  Atlantic  seaboard,  Chamberlin  for  the  Interior, 
Upham  for  Minnesota,  and  Wooster  for  Dakota.  Professor 
Wright's  investigations  extended  also  into  Indiana,  and  Cham- 
berlin's  stretched  from  New  Jersey  to  Dakota.  The  aggregate 


FORMATIONAL    GEOLOGY. 


449 


results  possess  extreme  interest,  and  are  mapped  on  a  small  scale 
in  Fig.  356. 

A  glance  at  this  map  shows  a  line  of  morainic  crescents  extend- 
ing from  Cape  Cod  along  or  near  the  southern  boundary  of  the 
Drift  area,  to  Indianapolis.  This  is  generally  regarded  as  a  line 
of  vestiges  of  the  terminal  moraine  of  the  earlier  glacier.  The 
more  northern  morainic  system  is  supposed  to  pertain  to  the  sec- 
ond glacier.  It  is  impracticable  here  to  enter  into  any  detailed 
description  of  these  moraines.  We  direct  attention  simply  to  a 
few  points,  (a)  The  older  moraine  does  not  border  the  Drift- 


FIG.  356. — MAP  OF  TERMINAL  MORAINE  TRACED  ACROSS  THE  UNITED  STATES. 
(Prom  Chamberlin's  Report.)    J3,  B,  J5,  Southern  Limit  of  Drift;  Jl/,  J/,  M,  Moraines. 

covered  area  west  of  Indiana,  (b)  It  is  not  coincident  with  that 
border  west^  of  Pennsylvania,  (c)  From  western  Pennsylvania 
to  Michigan  the  second  morainic  system  is  either  wanting  or  co- 
incident with  the  first  moraine,  or  quite  overlapped  it  and  oblit- 
erated it.  (d)  West  of  Lake  Erie  the  second  moraine  consists 
of  a  series  of  great  loops  rudely  concentric  with  the  great  lakes 
and  their  principal  bays.  It  may  be  added  that  the  directions  of 
the  glacial  striations  on  the  rocks  indicate  that  each  of  these 
principal  and  subordinate  basins  had  its  separate  glacier  sheet, 
which  formed  its  separate  loop  in  the  moraine  system,  (e)  The 


450  GEOLOGICAL   STUDIES. 

remarkable  northwesterly  trend  of  the  moraine  in  the  valley  of 
the  Missouri  River  follows  the  isothermal  lines,  (f)  A  broad,  drift- 
less  area  is  shown  in  Wisconsin.  (</)  Two  state  universities  are 
located  on  the  second  terminal  moraine.  The  University  of  Min- 
nesota is  located  near  the  junction  of  the  eastern  Lake  Superior 
and  northern  Minnesota  moraine.  The  University  of  Michigan 
is  on  the  interlobate  moraine,  between  the  Saginaw  and  Maumee 
glacial  lobes  —  the  Kames  rising  300  and  400  feet  above  the  bed 
rock,  and  the  "cat  hole"  within  the  city  limits  of  Ann  Arbor 
being  one  of  the  morainic  "kettles." 

(5).  Characteristics  of  the  Terminal  Moraine.  The  Termi- 
nal Moraine,  or  more  specifically  the  Second  Moraine,  consists  of 
an  extensive  irregular  range  of  confusedly  heaped  drift  ridges  or 
knolls.  It  sometimes  consists  of  two  or  more  separate  ranges, 
which  occupy  a  width  of  20  to  30  miles,  while  each  range  is  from 
one  to  six  miles  wide.  The  morainic  range  is  constituted  of  a 
series  of  hills  of  rapidly  but  gracefully  undulating  contour,  with 
rounded  domes,  conical  peaks,  winding  and  occasionally  genicu- 
lated  ridges,  short,  sharp  spurs,  mounds,  knolls,  and  hummocks 
promiscuously  arranged,  accompanied  by  corresponding  depres- 
sions. The  latter  are  variously  known  as  "potash  kettles,"  "pot 
holes,"  "pots  and  kettles,"  "cups  and  saucers"  (Fig.  7),  "sinks," 
etc.  The  characters  are  shown  in  the  accompanving  view  of  the 
moraine  near  Eagle,  Wis.  (Fig.  357).  These  characters  are  not 
fundamentally  different  from  those  presented  by  the  general  Drift. 
They  are  much  more  pronounced,  and  are  ranged  according  to  a 
discoverable  system. 

Internally,  the  moraine  is  distinguishable  into  two  portions. 
The  one,  usually  the  uppermost,  but  not  occupying  the  heights 
of  the  range,  consists  almost  wholly  of  assorted  and  stratified 
material,  resembling  the  modified  Drift  under  its  usual  and  famil- 
iar aspects  (Fig.  7).  The  other  element  of  the  moraine  consti- 
tutes its  basal  and  central  portion,  and  consists  of  a  confused 
commingling  of  clay,  sand,  gravel,  and  bowlders,  often  resembling 
true  subglacial  till.  It  is  probably  true  till  pushed  up  by  the 


FORMATIONAL   GEOLOGY.  451 

glacier,  acted   on   and   locally  assorted  and  stratified   by  waters 
escaping  from  the  glacier. 

(6)  Tabular  Limestone  Masses  Imbedded  in  the  Drift.  In 
certain  regions  —  notably  southern  Michigan,  in  the  counties  of 
Washtenaw,  Lenawee,  Hillsdale,  and  Jackson,  and  also  in  Ber- 
rien,  Van  Buren,  and  Ottawa  —  occur  numerous  tabular  masses  of 
limestone,  some  of  which  attain  dimensions  of  10  to  20  feet 
square  with  a  thickness  of  one  or  two  feet,  and  supply  material  for 
numerous  limekilns  of  a  transient  character.  These  masses  oc- 
cupy nearly  horizontal  positions,  and  lie  imbedded  near  the  sum- 


FIG.  357.— WESTERN  FACE  OF  THE  MORAINE  NEAR  EAGLE,  Wis.     (Chamberlin.)    Compare 

also  Fig.  5. 

mits  of  knolls  of  semistratified  sand.  They  are  fragments  of 
Corniferous  Limestone,  as  the  fossils  prove,  the  nearest  outcrops  of 
which  on  the  north  are  at  Mackinac,  and  on  the  south  within  the 
distance  of  10  to  30  miles.  They  have  not  the  worn  aspect  of 
bowlders;  they  have  been  transported  gently.  The  presumption 
is  that  they  have  been  derived  from  the  south.  The  present  writer 
suggested,  some  years  ago,  that  they  were  floated  by  ice  floes 
formed  over  shallow  lakes  accumulated  in  front  of  the  glacier 
during  the  period  of  retreat.  Chamberlin,  on  the  contrary,  has 
suggested  that  they  were  plowed  up  and  transported  by  the 
glacier,  and  made  part  of  the  terminal  moraine.  Similar  frag- 


452  GEOLOGICAL    STUDIES. 

ments  are  reported  from  Wisconsin.     The  explanation  of  these 
exceptional  facts  is  still  to  be  sought. 

(7)  Champlain  Deposits.     These  consist  chiefly  of  the  inco- 
herent stratified  materials  bordering  certain  lakes.     They  are  well 
shown  about  the  western  end  and  northern  border  of  Lake  Erie, 
whence  they  have  been  named  the   "Erie   clays."     They  occur 
also  over  the  western  part  of  the  peninsula  of  Ontario,  stretch- 
ing into   Michigan.     They   consist  of    layers   of    clay   and   sand 
mingled  with  some  vegetable  matter,  and  ascend  the  bordering 
slopes  sometimes  to  the  height  of  one  or  two  hundred  feet.     The 
lower  sandy  layers  rising  to  the  surface  become  saturated  with 
rain  water,  which  is  borne  along  the  dip  of  the  stratum,  and  thus 
furnishes  supplies   of   artesian    water   to   localities   at  the   lower 
levels. 

Other  extensive  Champlain  deposits  are  found  in  the  valley  of 
the  Red  River  of  the  North.  They  were  laid  down  in  a  former 
great  lake,  which  Mr.  Warren  Upham  proposes  to  call  Lake 
Agassiz.  The  shore  lines  may  still  be  traced  at  various  levels  on 
the  east  and  west.  The  lake  must  have  received  the  waters  of 
the  Saskatchewan,  and  had  its  outflow  southward  to  the  Mis- 
sissippi. 

Evidently  the  sediments  bordering  Lakes  Erie  and  Michigan 
were  laid  down  when  the  lakes  stood  at  higher  levels.  As  to  the 
drainage  and  diminution  of  lakes,  it  seems  to  have  been  general. 
The  climate  of  America  has  grown  dryer  in  late  geological  epochs. 
But  undoubtedly  much  lake  drainage  has  resulted  from  a  wearing 
down  of  outlets.  Apparently  this  cause  has  operated  upon  Lakes 
Erie,  Huron,  and  Michigan,  as  was  explained  when  treating  of 
the  Niagara  gorge.  Fig.  305  may  now  be  further  studied. 

(8)  Quaternary  Lakes.     In  the  Basin  Province   of   the  Far 
W^est  we  find  the  remnants  of  ancient  Quaternary  lakes,  which 
far  exceeded  present  limits.     Their  former  bounds  are  shown  by 
old  beach  lines.     These  lakes  —  of  which  Lahontan  and  Bonne- 
ville  are  best  known,  thanks  to  the  labors  of  Gilbert  and  King  — 
resulted  originally  from  the  subsidence  of  the  east  and  west  sides 
of  the  Basin,  which  took  place  at  the  end  of  the  Pliocene.      The 


FORMATIONAL   GEOLOGY.  453 

bottoms  of  the  depressions  formed  were  4,000  feet  above  sea 
level,  and  their  borders  5,000  feet.  Vestiges  of  Lake  Bonneville 
are  seen  at  present  in  Great  Salt  Lake,  Utah  Lake,  and  Sevier 
Lake.  This  lake  was  300  miles  long  and  180  miles  broad.  The 
highest  terrace  is  940  feet  above  the  present  level  of  Great  Salt 
Lake.  Lake  Lahontan  lay  in  western  Nevada,  along  the  bold 
front  of  the  Sierra,  and  was  nearly  as  large  as  the  former;  but  it 
was  much  cut  up  by  mountain  ranges.  Remnants  of  this  lake  are 
still  seen  in  Pyramid,  Winnemuca,  Carson,  Walker,  and  Humboldt 
Lakes.  These  great  ancient  lakes  began  to  exist  with  the  begin- 
ning of  Quaternary  time  —  though  Lahontan  was  a  smaller  lake 
during  the  Miocene  —  but  the  progress  of  their  desiccation  con- 
tinued into  the  Champlain  epoch;  and  some  evidences  exist  that 
it  continued  till  near  the  present.  The  water  of  Great  Salt  Lake, 
however,  rose  eleven  feet  between  1849  and  1878.  But  it  was 
nearly  constant  till  1866,  and  the  rise  is  a  later  occurrence. 
King  is  of  the  opinion  that  the  salinity  of  these  lakes  is  derived 
from  the  influx  of  saline  waters.  If,  as  Gilbert  and  King  have 
shown,  they  formerly  had  drainage  to  the  sea,  their  primitive 
salinity  derived  from  the  influx  of  ocean  water  must  have  been 
exhausted;  they  were  fresh- water  lakes  during  their  high  level; 
and  since  the  outflow  ceased,  the  only  probable  source  of  their 
present  salinity  is  the  slight  saline  contribution  brought  by  tribu- 
tary streams.  Though  these  lakes  are  generally  considered  coeval 
with  eastern  glaciation,  it  remains  to  show,  with  plausibility,  that 
they  were  not  rather  a  feature  of  the  Champlain  Epoch. 

In  the  northwestern  part  of  the  Great  Basin,  in  Oregon,  other 
Quaternary  lakes  have  been  described  by  Russell.  These  occu- 
pied the  sites  of  the  present  lakes,  Alvord,  Malheur,  Warner, 
Guano,  Summer,  Abert,  Silver,  Goose,  and  Klamath,  in  Oregon, 
together  with  Surprise  Valley  and  the  Madeline  Plains  in  Cali- 
fornia, and  Long  Valley  in  Nevada.  Some  of  them  attained  a 
depth  of  500  and  600  feet,  and  spread  far  beyond  the  limits  of  the 
modern  lakes.  In  the  old  bed  of  Christmas  Lake  are  found  many 
modern  species  of  fresh-water  shells,  together  with  bones  of 
mammals  reported  by  Marsh  as  Pliocene, —  and  thus  possibly 


454  GEOLOGICAL   STUDIES. 

washed  in  after  fossilization.  These  lakes  lie  between  the  117th 
and  121st  meridians,  and  extend  from  the  parallel  41°  to  43°  30'. 
Directly  north  of  this  group  of  lakes,  between  the  parallels  of  46° 
and  47°  30',  is  the  bed  of  another  ancient  lake,  designated  Lake 
Lewis  by  Lieutenant  Symonds,  who  regards  the  lake  as  of 
Champlain  age. 

(9)  Recent  Formations.  River  terraces  and  some  other 
phenomena  of  the  latest  epoch  of  geological  history  have  been 
sufficiently  considered  in  Part  I,  Study  XV.  River  terraces  are 
illustrated  in  Fig.  210. 

The  geological  work  of  the  Recent  or  Terrace  Epoch  em- 
braces much  more  than  the  formation  of  terraces,  as  commonly 
understood.  Since  the  dissolution  of  the  continental  glaciers, 
the  drainage  of  the  land  has  become  settled  in  its  courses,  and 
all  the  depositions  which  rest  on  the  Modified  Drift  have  been  laid 
down.  River  deltas  have  been  formed  in  all  their  extent.  The 
drainage  of  lakes  has  continued,  and  innumerable  small  lakes 
have  been  filled  with  beds  of  marl  and  peat,  as  previously  ex- 
plained, page  82  and  Fig.  25.  The  beds  of  rivers  have,  in  many 
instances,  been  sunken  by  erosion,  though  in  others  the  shrink- 
age of  the  volume  of  water  has  caused  them  to  rise  by  accumu- 
lation of  sediment.  Cavern  erosions  have  been  continued,  though 
more  frequently  the  diminution  of  water  has  arrested  the  work 
of  cavern  making.  The  formation  of  stalagmites  and  stalactites 
dates,  generally,  from  the  Glacial  epoch,  or  even  an  older  one. 
This  is  true  of  much  of  the  work  which  we  witness  in  progress. 
The  erosion  of  gorges  is  generally  a  process  of  which  we  witness 
only  the  latest  stages.  The  excavation  of  caverns  must  have  been 
begun  as  soon  as  the  land  drainage  found  fissures  in  limestone 
formations  through  which  to  flow.  The  removal  of  soils  and  the 
exposure  of  underlying  rocks  has  been  in  progress  as  long  as 
land  has  existed.  In  some  cases  the  work  was  completed  and  the 
land  obliterated  even  before  the  modern  epoch. 

The  drainage  valleys  and  the  deep-cut  gorges  with  which  we 
are  familiar  in  the  topography  of  the  present  epoch  are  largely 
results  which  have  been  in  progress  as  long  as  the  land  surfaces 


FORMATIO^AL   GEOLOGY. 


455 


have  been  exposed.  Some  of  these  works  extend  back,  probably, 
into  Palaeozoic  time;  but  some  of  the  greatest,  like  the  canon  of 
the  Colorado,  have  been  accomplished  since  late  Tertiary  time,  as 
is  proved  by  the  age  of  the  strata  excavated.  The  valleys  of  the 
Hudson  and  Connecticut  may  date  from  the  Palaeozoic;  but  if  so, 
their  courses  were  both  interrupted  by  the  deposits  and  the  oro- 
graphic  movements  of  the  Triassic;  to  be  reopened  after  the 


FIG.  358.— SUBMARINE  CHANNEL  OF  THE  HUDSON  RIVER  AND  THE  ANCIENT  ATLANTIC 
SHORE.     (After  Lindenkohl.) 

close  of  the  Triassic.  The  actual  submarine  shore  line  of  the 
coast  of  the  United  States,  Fig.  358,  is  a  feature  in  modern  topo- 
graphy. It  lies  from  80  to  100  miles  from  the  present  shore,  in 
about  500  feet  of  water.  Off  the  harbor  of  New  York,  we  find 
what  appears  to  be  an  ancient  channel  of  the  Hudson  River  con- 
tinued seaward  when  the  land  was  some  hundreds  of  feet  higher. 
This  may  have  been  excavated  as  far  back  as  Palaeozoic  time, 
when  the  Seaboard  Land  had  its  higher  altitude,  and  may  have 


456  GEOLOGICAL   STUDIES. 

gone  down  with  the  eastern  border  of  that  land,  when  the  Appal- 
achian border  reemerged.  The  submerged  Hudson  channel, 
whenever  formed,  extends  80  miles  to  sea.  At  the  distance  of  10 
miles  its  bottom  is  48  feet  below  the  general  sea  bottom.  At  20 
miles  it  is  90  feet  below.  At  50  miles  it  is  66  feet,  and  continues 
to  diminish.  At  80  miles  is  an  ancient  bar.  The  width  of  the 
channel  is  three-fourths  of  a  mile  to  a  mile.  Beyond  the  bar  is 
what  appears  like  an  ancient  fiord,  beginning  about  85  miles  from 
Sandy  Hook,  and  extending  25  miles  to  the  edge  of  the  conti- 
nental slope,  with  a  width  of  about  three  miles.  For  half  its 
length  this  ravine  has  a  depth  of  over  2,000  feet.  It  is  inter- 
rupted by  a  bar  1,600  feet  high.  The  sides  of  this  submarine 
river  channel  slope  at  an  angle  of  one  to  three  degrees;  those  of 
the  fiord,  14°. 

In  the  changes  progressing  under  our  observation  we  are  fur- 
nished with  clews  to  the  explanation  of  the  grander  events  of 
remote  geological  history.  To  a  large  extent  these  are  but  ag- 
gregates of  slow  operations  continued  through  geologic  aeons. 
So  far  the  method  has  been  uniformitarian.  In  the  elevation  of 
the  Uintas  we  witness,  undoubtedly,  as  Powell  has  demonstrated, 
a  grand  result  accomplished  by  slow  movements,  since  the  Green 
River  has  cut  through  the  whole  altitude  of  the  range.  But  some 
cataclysmic  events  must  have  taken  place,  as  convulsions  like 
those  of  Kra-kat'oa,  Ischia,  and  Andalusia,  in  our  own  day,  would 
indicate.  Much  greater  ones,  but  of  the  same  order,  must  have 
occurred  when  the  Wahsatch  and  Sierra  Nevada  were  rent  longi- 
tudinally, and  the  Basin  Province  sank  a  thousand  feet  along  each 
of  its  borders.  On  the  whole,  however,  the  geological  work  in 
progress  may  be  regarded  as  mirroring  the  nature  of  the  methods 
of  the  operations  which  have  formed  the  world.  Assuming  that 
the  same  modes  of  activity  will  continue  in  the  remote  future, 
we  have  ground  for  anticipating  unrealized  results  as  grand  and 
transforming  as  any  which  have  been  realized  in  the  history  of 
the  past. 

(10)    Organic  Remains  of  the  Quaternary.     In  the  ordinary 
glacial  Drift  few  relics  of  the  organization  of  the  epoch  occur. 


FORMATIOXAL   GEOLOGY.  457 

Yet  pieces  of  white  cedar  are  found  at  various  depths  down  to 
60  feet  at  least,  in  the  modified  Drift.  In  regions  south  of  the 
glacial  limits  life  continued  to  nourish  —  both  on  the  land  and  in 
fresh  waters.  The  great  Quaternary  Lakes  Bonneville  and  La- 
hontan  (whether  Glacial  or  Champlain)  on  the  eastern  and  west- 
ern sides  of  the  Great  Basin,  were  stocked  with  fresh-water 
species  of  molluscs,  of  which  the  most  abundant  genera  were 
Limncea,  Pomatiopsis,  Amnicola,  and  Succmea.  The  Oregon 
Quaternary  lakes  were  similarly  inhabited.  In  the  Champlain 
epoch  the  Gulf  of  St.  Lawrence  extended  into  the  basin  of  Lake 
Champlain;  and  some  molluscan  remains  have  been  left  in  the 
valley  of  the  St.  Lawrence,  in  the  "Leda  clays."  The  skeleton 
of  a  small  white  whale,  JSeluga  Vermontana,  has  been  discovered 
on  the  borders  of  Lake  Champlain. 

Of  land  mammals  numerous  species  have  been  found  in  cav- 
erns and  rock  fissures,  and  in  post-glacial  surface  deposits.  The 
age  of  remains  from  caverns  and  fissures  may  be  glacial  or  post- 
glacial; but  remains  in  beds  resting  on  the  Drift  must,  of  course, 
belong  to  the  Champlain  epoch,  if  of  extinct  species,  or  to  the 
Recent  epoch,  probably,  if  of  living  species.  A  limestone  fissure 
at  Port  Kennedy,  Pa.,  has  afforded  Cope  remains  of  34  species  of 
mammals,  mostly  extinct.  Caves  in  Wythe  county,  Va. ;  at  Ga- 
lena, 111. ;  and  near  Carlisle,  Pa,,  have  afforded  many  remains,  some 
of  which  belong  to  extinct  species. 

In  deposits  more  recent  than  the  Glacial  epoch  have  been 
found  remains  of  a  species  of  Elephant  ( Elephas  Americanus 

—  the  same  as  Elephas  or  Euelephas  Jacksoni)  as  large  as  the 
Quaternary  Elephant  of  the  Old  World.     The  latter  also  (Ele- 
phas primige'nius)  is  found  in  the  more   northern   latitudes  of 
America  (see  Fig.  364).     More  frequent  is  the  Mastodon  —  Mas- 
todon Americanus  (called  also  M.  giganteus  and  M.   Ohioticus) 

—  found  generally  in  peat  bogs  where,  according  to  prevailing 
opinion,  the  creature  became  mired.     But  the  carcass  may  also 
have  been  borne  in  by  a  flood  while  the  bog  was  yet  a  lake.     The 
Mastodon  was  abundant  throughout  the  Northern  United  States. 
Three  perfect  skeletons  have  been  exhumed  in  Orange  county, 


458 


GEOLOGICAL   STUDIES. 


New  York;  one  near  Cohoes  Falls  on  the  Mohawk,  one  in  New 
Jersey,  one  in  Indiana  (destroyed  in  the  great  Chicago  fire),  and 
one  from  the  banks  of  the  Missouri.  Skeletons  imperfectly  pre- 
served have  been  found  in  very  numerous  localities,  especially 
western.  A  nearly  complete  skeleton  was  exhumed  near  Tecum- 
seh,  Mich.,  and  another  in  Cass  county.  Dr.  Warren's  Mastodon 
from  near  Newburgh  has  a  height  of  11  feet,  with  a  length  of  17 
feet  to  the  base  of  the  tail.  The  tusks  are  12  feet  long,  of  which 
2-|  feet  are  inserted  in  the  sockets.  The  total  height  when  living 


FIGS.  359-362.  —  PLAN  or  ENAMEL  PLATES  ON  THE  MOLAB  CROWNS  OF  PROBOSCIDIANS. 
359,  Molar  of  African  Elephant;  360,  Indian  Elephant;  361,  Mammoth;  362,  Molar 
of  Mastodon,  perspective  view. 

must  have  been  12  or  13  feet,  and  the  length  24  or  25  feet,  The 
Mastodon  probably  survived  to  the  recent  epoch.  The  Tecumseh 
Mastodon  was  buried  in  a  small  bog  with  only  18  inches  of  peat 
over  it.  In  the  same  county  Indian  arrow  heads  are  found  seven 
feet  beneath  the  surface  of  the  peat.  Mastodon  remains  are  re- 
ported in  Florida,  south  of  the  thirtieth  parallel. 

The  most  striking  differences  between  the  elephant  and  mas- 
todon are  found  in  the  molar  teeth;  and  these  are  illustrated  in 
Figs.  359  to  362. 

The  post-glacial  deposits  of  North  America  have  afforded  also 


FORMATIO^AL   GEOLOGY.  459 

the  remains  of  a  Horse,  larger  than  the  domestic  species,  a  gi- 
gantic Beaver  (Castoroides  Ohioensis],  of  which  an  incisor  is 
shown  reduced  in  Fig. 
363;  pig-like  and  pec- 
cary -  like  animals; 
Oxen,  Bisons,  and 
Tapirs  •  also  Bears, 
Lions,  and  Raccoons. 
Some  Edentates,  in  our 
times  almost  peculiar 
to  South  America,  ex- 

A      A      fV»    '  FlG"  36:*-~ INCISOR  OF  THE  EXTINCT  GIGANTIC  BEAVER 

tneir    range         (Casf  or  aides  Ohioensis).    From  Lapeer,  Mich,     x  Y2. 
northward  to  the  Ohio 

River.  They  include  several  species  of  Megal'onyx,  and  one  each 
of  Myl'odon  and  Megatherium.  From  Florida  are  reported  re- 
mains of  Rhinoceros,  Stag,  Camel,  Tapir,  and  Hippopotamus. 

In  South  America  Edendates  were  the  predominant  ordinal 
type,  as  they  still  are.  The  pampean  formation  of  the  southern 
part  of  the  continent  is  a  vast,  level  deposit,  20  to  100  feet  deep, 
formed  largely  of  materials  borne  eastward  from  the  slopes  of 
the  Andes  at  a  time  when  the  Atlantic  covered  the  country  to 
the  foot  of  the  mountains.  It  stretches  over  the  larger  part  of 
Patagonia  and  the  Argentine  Republic,  embracing  one  and  a  half 
million  square  miles.  This  Quaternary  formation  is  a  literal  cem- 
etery of  strange  and  mostly  uncouth  mammalian  forms.  The 
great  Megatherium  Cuvieri  (Fig.  364)  was  larger  than  the  Rhi- 
noceros, and  in  some  of  its  proportions  exceeded  the  elephant. 
The  femur  was  three  times  as  thick  as  the  elephant's.  This  ani- 
mal was  a  huge  ground  sloth,  with  massive  posterior  extremities 
and  post-like  tail,  which  suggests  its  probable  habit  of  standing 
erect  to  browse  from  the  foliage  of  the  forest.  Other  and  asso- 
ciated Edendates  were  Megal'onyx,  so  named  by  President  Jeffer- 
son ;  Myl'odon,  larger  than  the  American  buffalo ;  Scelidothe'- 
riuni,  an  allied  genus,  and  Glyp'todon,  a  huge  armadillo,  cara- 
pace-covered like  a  turtle. 

In  Europe,  the  oldest  Quaternary  relics  are  found  in  caverns. 


460 


GEOLOGICAL   STUDIES. 


They  embrace  the  Cave  Bear,  Cave  Hyaena,  and  Cave  Lion,  all 
somewhat  larger  than  the  nearest  related  modern  species,  but  all 
regarded,  at  present,  as  identical  with  modern  species,  or  derived 
from  them.  With  these  are  found  bones  of  the  Mammoth  (Ele- 
phas  primigenius),  Rhinoceros,  Hippopotamus,  Deer,  Aurochs, 
or  European  Bison,  and  other  species,  and  often  implements  of 


FIG.  SW.—Megathe'rium  Cum'eri,  RESTORED.    From  the  Pampas  near  Buenos  Ayres. 

human  production.  The  most  celebrated  bone  caverns  are  those 
of  Kirkdale,  Kent's  Hole,  and  Brixham,  in  Great  Britain,  and 
Gailenreuth,  Perigord,  and  the  Bordogne,  on  the  continent. 

The  Mammoth  extended  into  Siberia,  and  thence  into  Alaska. 
The  tusks  exist  in  such  abundance  as  to  constitute  an  article  of 
export.  The  carcass  of  the  Mammoth  is  sometimes  found  im- 
bedded in  permanent  ice.  In  some  cases  the  flesh  is  thus  pre- 


FORMATIONAL   GEOLOGY. 


461 


served,  and  supplies  food  for  dogs,  wolves,  and  foxes.  In  one 
celebrated  instance,  a  carcass  taken  from  ice  near  the  mouth  of 
the  Lena  furnished  a  skeleton  which  was  mounted  in  the  Museum 
at  St.  Petersburg.  From  this,  and  other  bones  discovered  in 
Europe,  Dr.  Frass,  of  Stuttgardt,  effected  a  restoration  which  is 
now  in  Ward's  Natural  History  Establishment,  at  Rochester,  N. 
Y.  Of  this,  a  representation  is  giyen  in  Fig.  365.  It  will  be 


FIG.  365.  — RESTORATION  OF  THE  SIBERO-AMERICAN  MAMMOTH   (Elephas  primigenius). 
(After  Fraas  and  H.  A.  Ward.) 

noticed  that  this  elephant  was  warmly  clad  with  hair  of  three 
kinds.  The  most  abundant  was  reddish  wool,  an  inch  in  length. 
Interspersed  through  this  were  reddish-brown  hairs,  four  inches 
long,  and  sparser  black  bristles,  twelve  to  sixteen  inches  long. 
It  is  reasonable  to  infer  from  the  clothing  that  the  mammoth 
inhabited  a  cold,  or  a  cold-temperate  climate  in  the  epoch  before 
the  advent  of  continental  glaciers.  It  appears,  too,  that  the 
invasion  of  snow  and  permanent  cold  was  sudden.  The  mam- 


462  GEOLOGICAL   STUDIES. 

moth  had  no  time  for  retreat.  There  was  no  returning  spring- 
time. The  beast,  once  buried,  remained  frozen  through  a  geologic 
period. 

It  has  been  believed  that  the  mammoth  had  become  extinct; 
but  the  mountains  of  Siam  have  yielded  at  least  two  young  spec- 
imens of  a  hairy,  perhaps  dwarf,  elephant,  which  seems  clearly  to 
be  the  descendant  of  the  mammoth  of  the  North.  These  ele- 
phants were  imported  into  New  York  in  1884. 

Human  implements  and  human  bones  are  found  in  European 
caverns,  in  interglacial  deposits  and  in  river  drifts,  associated 
with  the  relics  of  extinct  mammals.  It  appears  from  the  evi- 
dences that  man,  in  a  barbarous  state,  was  a  resident  in  Europe 
as  early  as  the  interglacial  epoch.  Some  indications  of  his  pres- 
ence during  the  Pliocene,  and  even  the  Miocene,  period,  have 
been  thought  to  exist;  but  the  general  opinion  holds  as  insuffi- 
cient the  alleged  evidence  of  his  preglacial  advent, 


CHAPTER  VI. 
HISTORICAL  GEOLOGY; 

OR,  WHAT  HAS  BEEN  LEARNED  ABOUT  GEOLOGICAL  PROGRESS. 

§  1.      Presedimentary  History. 

ALL  that  can  be  said  about  the  history  of  terrestrial  matter 
during  aeons  antecedent  to  the  formation  of  enduring  record- 
bearing  rocks  must  be  a  deduction  from  (1)  The  ascertained  laws 
of  matter;  (2)  The  conditions  observed  in  other  worlds;  (3)  The 
principles  of  world  making  disclosed  in  the  rocky  records  of  our 
planet.  It  is  intended  to  offer  only  a  few  condensed  statements. 

It  is  generally  believed  that  the  matter  of  the  earth  and  the 
whole  solar  system  existed,  at  a  very  remote  period,  in  a  condi- 
tion analogous  to  that  of  modern  nebulae.  These  probably  consist 
of  particles  and  masses  accumulated  through  the  action  of  gravi- 
tation, from  wide  realms  of  space.  Through  the  processes  of 
aggregation,  heat  and  rotation  are  generated  in  the  nebula. 
Our  solar  nebula  was  once  in  such  a  state.  Through  cooling  and 
shrinkage,  its  rotation  was  accelerated,  until  a  succession  of  rings 
was  detached,  each  of  which,  in  the  course  of  time,  assumed  the 
form  of  a  planet.  Each  planet  was  at  first  in  the  condition  of 
discrete  matter  of  high  mobility,  and  in  a  state  of  rotation. 
Some  of  them,  in  turn,  detached  rings,  which  became  satellites. 

At  some  stage  in  the  process  of  cooling,  a  portion  of  the 
matter  of  a  planet,  or  the  whole  of  it,  existed  in  the  condition  of 
''fire-mist,"  or  liquid  particles  of  mineral  matter,  enveloped  in 
other  matter  retaining  the  gaseous  condition.  Such  was  once 
our  earth.  At  a  later  stage,  however,  the  mineral  particles 
descended  toward  the  centre  of  gravity,  and  the  planet  became 
a  molten  globe.  Enormous  pressure  at  the  centre  may  have 

463 


464  GEOLOGICAL   STUDIES. 

reduced  the  central  portion  to  a  solid  state;  but  this  solidity  was 
of  a  very  different  nature  from  that  which  resulted  from  cooling 
at  the  surface.  From  superficial  cooling1,  a  solid  crust  resulted, 
and  this  thickened  continually. 

In  the  course  of  time,  but  probably  while  the  crust  still 
retained  an  incandescent  temperature,  the  vapor  of  water  began 
to  condense  in  the  higher  atmosphere.  Before  this,  water  could 
only  exist  in  an  invisible  gas.  Clouds  now  gathered  around  the 
world,  and  the  first  rains  descended,  amid  scenes  of  terrific  elec- 
trical disturbance.  The  falling  rains  hastened  the  thickening  of 
the  crust  and  the  cooling  of  the  surface;  and  in  the  course  of  a 
geologic  age,  water  was  permitted  to  accumulate  in  a  film,  which 
constituted  a  universal  ocean.  The  descending  rains  had  washed 
down  the  atmospheric  acids,  and  the  ocean  was  one  of  acid 
waters.  These  waters  were  hot.  They  rested  on  a  crust  which, 
from  its  mode  of  origin,  was  alkaline,  and  was  ready  to  undergo 
chemical  change  as  soon  as  an  acid  solution  was  brought  in  con- 
tact with  it.  In  this  ocean  chemical  action  was  intense.  The 
results  were  soluble  substances,  like  chlorides  and  sulphates,  left 
in  solution,  and  other  substances,  like  silicates  and  calcium  car- 
bonate, precipitated.  Thus  precipitates  accumulated  over  the 
ocean  bottom;  and  to  these  were  added  such  detritus  as  resulted 
from  the  mechanical  action  of  the  ocean  in  the  shallowest  situa- 
tions. The  thickened  crust  impeded  the  escape  of  internal  heat, 
and  this  acted  on  the  under  side  of  the  crust,  re-fusing  some 
portions,  to  restore  the  equilibrium  thickness. 

Thus  the  cooling,  so  long  in  progress,  continued.  But  the 
crust  did  not  cool  in  the  same  proportion  as  the  internal  mass; 
and  wrinkles  resulted.  These  assumed  general  meridional  trends 
in  consequence  of  ingrained  predeterminations,  caused  by  tidal 
actions  during  the  incrustive  stage,  and  by  the  progressive  secu- 
lar subsidence  of  the  earth's  equatorial  protuberance,  resulting 
from  the  slow  diminution  of  rotational  velocity.  These  wrinkles, 
whether  submerged  or  emergent,  furnished  the  waves  new  oppor- 
tunities for  detrital  production.  Thus  the  crust  thickened  at  an 
increased  rate  in  the  more  deeply  submerged  regions,  and  the 


HISTORICAL   GEOLOGY.  465 

removal  of  subjacent  layers  proceeded.  What  amount  of  the 
original  crust  may  have  been  re-fused  in  this  way  can  only  be 
conjectured.  As  no  portion  of  the  original  fire-formed  crust  has 
ever  been  discovered,  we  may  infer  that  it  was  all  returned  to 
the  molten  interior.  We  may  even  conclude  with  probability 
that  much  of  the  super-crust,  or  stratified  crust,  was  also  re-fused; 
since  the  lowest  strata  yet  explored  fail  to  reveal  the  evidences 
of  violent  oceanic  movements  which  must  have  taken  place  when 
the  moon  was  much  nearer  the  earth,  and  produced  much  greater 
tides,  while,  at  the  same  time,  the  terrestrial  day  was  shorter. 
When  those  sediments  were  deposited  which  have  formed  the 
oldest  Laurentian  rocks,  the  tidal  and  other  physical  forces 
appear  to  have  been  acting  very  much  as  in  our  times. 

§  2.     Inductive  History. 

1.  The  Eozoic  ^Eon.  The  visible  rocks  reveal  a  body  of 
facts  from  which  we  may  reason  by  inductive  inference,  as  well 
as  from  the  principles  of  nature.  The  history  thus  far  deduced 
brings  us  down  to  the  Eozoic  ^Eon.  To  this  Great  System  belong 
the  oldest  rocks  preserved  for  our  study.  There  must  have  been 
sources  of  sediments  then  in  existence,  for  these  rocks  are  sedi- 
mentary in  their  nature,  though  the  oldest  cannot  be  pronounced 
characteristically  fragmental.  If  there  were  any  emergent  lands 
during  Eozoic  time,  we  know  not  where  they  were.  They  have 
disappeared,  consumed  by  the  erosions  which  were  preparing 
materials  for  the  continental  foundations  of  later  ages.  Perhaps 
the  ocean  was  still  universal,  and  the  erosions  were  suffered  by 
the  shallower  portions  of  the  sea  bottom.  The  rocks  which 
resulted  are  before  us,  bearing,  however,  the  marks  of  subsequent 
metamorphism,  to  an  uncertain  extent.  We  have  passed  these 
rocks  in  review.  They  overstrew  the  drift-covered  surfaces. 
The  deepest  rocks  are  also  very  extensively  the  surface  rocks. 

With  the  progress  of  time,  the  conditions  of  rock  formation 
changed.  We  have,  in  the  same  regions,  gneisses,  slates,  con- 
glomerates, and  limestones,  piled  successively  above  each  other. 
What  was  the  nature  of  these  changes  we  will  not  stop  to  inquire. 


466  GEOLOGICAL   STUDIES. 

We  know,  to  a  certainty,  that  the  Eozoic  ^Eon  was  inconceiva- 
bly long;  and  that  the  ocean  reigned  almost  or  quite  universally. 

Of  life  during  the  earlier  ages,  there  was  none.  At  length 
arrived  a  humble  form,  which  planted  itself  upon  the  sea  bottom, 
and  opened  the  drama  of  organization.  Of  Eozo5n,  in  its  struc- 
ture and  affinities,  we  have  learned  in  another  connection.  It 
was  the  reef  builder  of  these  twilight  ages.  But  when  Eozoo'n 
ceased  to  live  and  work  there  was  a  blank,  so  far  as  observation 
goes.  In  the  Upper  Laurentian  and  Huronian,  no  trace  of  organ- 
ization has  been  discovered.  We  cannot  admit,  however,  that 
life,  once  introduced,  was  permitted  to  become  extinct,  and  thus 
create  the  necessity  of  a  new  beginning.  We  must  conclude 
that  the  processes  of  metamorphism,  which  so  transmuted  many 
of  the  rocks,  have  completely  obliterated  all  fossil  remains. 
Probably  the  Huronian  rocks  once  contained  the  records  of  Hu- 
ronian life. 

But  of  the  physical  vicissitudes  of  Eozoic  time  we  can  say 
more.  The  crustal  wrinkling  before  mentioned  was  part  of  a 
method  which  was  destined  to  be  continued.  Sediments  of  Lau- 
rentian age,  hardened  already  by  chemical,  thermal,  and  mechan- 
ical actions,  were  mashed  together  by  lateral  pressure,  crumpled 
where  they  could  not  be  mashed,  and  uplifted  in  huge  folds 
when  the  surplusage  of  circumference  became  too  great  to  be 
disposed  of  by  these  methods.  In  other  words,  Laurentian  folds 
of  the  crust  rose  toward  or  above  the  surface  of  the  ocean. 

Meantime,  deposition  proceeded.  The  new  folds  began  to  be 
worn  down,  and  later  deposits,  known  as  Huronian,  rested  un- 
conformably  on  them.  There  were  probably  other  uplifts  of  the 
primal  folds.  If  we  reason  correctly,  it  was  yet  Eozoic  time 
when  the  Keweenian  formations  came  into  existence.  In  the 
region  which  has  since  been  the  basin  of  Lake  Superior,  igneous 
ejections  occurred  on  a  scale  of  great  magnitude.  Probably  the 
region  had  become  land  through  an  uplift  at  the  close  of  the 
Huronian.  Over  this  area,  great  sheets  of  molten  lava,  welling 
through  the  broken  crust,  spread  out  for  a  distance  of  300  miles 
from  east  to  west,  and  100  miles  from  north  to  south.  The  crust 


HISTORICAL   GEOLOGY.  467 

began  to  sink,  as  if  a  void  had  been  produced  beneath  it.  The 
sea  returned,  and  covered  the  region.  From  the  adjoining  fel- 
sitic  slopes  large  quantities  of  fragments  were  broken,  and  rolled 
as  pebbles  over  the  sunken  lava  sheet,  till  the  surface  became 
again  dry  land,  or  a  mere  shallow.  Then  the  molten  eruption 
recurred,  and  again  a  sinking  was  experienced.  These  outflows 
and  subsidences,  and  interposed  sedimentary  sheets,  were  many 
times  repeated. 

The  close  of  the  Eozoic  JRon  now  approached.  Great  sub- 
marine wrinkles,  grouped  in  some  cases  in  wide  and  massive  sys- 
tems, had  been  for  ages  rising  to  the  surface  of  the  ocean,  and 
above  its  surface.  The  germinal  areas  of  the  North  American 
continent  had  now  emerged.  The  chief  of  these  were  three.  (1) 
The  Laurentian  or  Great  Northern  Land.  This  consisted  of  an 
irregularly  arcuate  ridge  or  broad  mountain  elevation  encompass- 
ing the  area  now  occupied  by  Hudson's  Bay.  Its  longer  limb 
stretched  from  the  northern  shore  of  Lake  Huron,  as  it  now 
exists,  northwestward  between  Hudson's  Bay  and  the  MacKenzie 
River  to  the  Arctic  Ocean;  while  the  shorter  limb  stretched  from 
the  same  region  northeastward  to  the  coast  of  Labrador.  (2) 
The  Seaboard  Land.  This  was  a  broad,  crushed,  and  plicated 
swell  or  mass  of  wrinkles,  stretching  from  Maine  southwestward 
to  Alabama,  along  the  slope  between  the  present  Appalachians 
and  the  Atlantic  Ocean.  There  is  considerable  reason  to  believe 
that  in  breadth  it  embraced  the  region  which  was  destined  in 
later  ages  to  become  the  site  of  the  Appalachian  chain  of  mount- 
ains, though  in  the  intervening  time  destined  to  undergo  a  long 
submergence.-  There  is  equal  reason  to  conclude  that  this  land 
extended  eastward  beyond  the  present  Atlantic  shore,  perhaps  to 
the  brink  of  the  slope  into  the  deep  sea.  These  conjectural 
dimensions  are  represented  in  the  JEonic  Map,  Fig.  297.  (3) 
The  Cordilleran  Land.  This  was  the  western  germinal  area.  In 
width  it  stretched  from  the  eastern  base  of  the  Rocky  Mountains 
westward  into  eastern  California,  a  distance  of  750  miles  along 
the  parallel  of  40°.  It  extended  great,  but  unknown  distances 
northward  and  southward.  This  land  was  a  great  mountain  sys- 


468  GEOLOGICAL   STUDIES. 

tern,  displaying  lofty  ranges  made  of  crumpled  strata;  mechanical 
dislocations  effected  on  a  most  gigantic  scale,  but  withal  a 
smoothness  of  surface  contour,  and  an  absence  of  deep  canons 
and  worn  gulches  which  seems  to  argue  an  absence  of  those 
methods  of  erosion  which  have  determined  the  configuration  of 
the  modern  surface.  This  massive  belt  of  Eozoic  Cordilleras 
determined  the  limits  of  the  modern  Cordilleras,  and  very  much 
of  the  details  of  their  fundamental  structure. 

2.  The  Palceozoic  ^Eon.  (1)  Movements  of  the  Lands.  It 
was  now  a  new  morning  in  the  world's  history.  The  Cambrian 
Age  was  dawning.  The  corner  stones  of  the  continent  had  been 
deeply  laid;  yet  over  the  site  of  North  America  an  ocean  ex- 
panse still  brooded.  The  transition  from  Eozoic  to  Palaeozoic 
time  was  marked  by  important  orographic  movements.  While 
the  Great  Northern  Land  stood  unmoved,  the  Seaboard  and  Cor- 
dilleran  lands  underwent  great  subsidence.  The  western  part  of 
the  former  and  the  eastern  part  of  the  latter  went  down  beneath 
sea  level;  and  Palaeozoic  sediments  began  to  be  spread  out  over 
them.  Of  the  Seaboard  Land,  the  Appalachian  site  became  sub- 
merged. Of  the  Cordilleran  Land,  all  subsided  from  the  region 
of  the  Great  Plains  to  eastern  California.  Only  the  granitic 
mountain  summits  stood  emergent.  The  broad  continent  had 
become  an  archipelago.  Highest  stood  the  Colorado,  Medicine 
Bow,  and  Park  ranges,  on  the  eastern  border  of  the  sunken  land. 
The  continental  mass  remaining  was  on  the  western  border.  It 
was  destined  to  be  wasted  in  yielding  the  materials  to  be  spread 
over  the  ocean  bottom,  for  the  upbuilding  of  the  Palaeozoic  for- 
mations. While  this  sunken  Cordilleran  surface  was  receiving 
its  load,  it  continued  to  sink.  But  as  the  coarsest  and  most 
copious  deposition  was  near  the  wasting  Nevada  Land  which 
yielded  the  materials,  the  subsidence  was  greatest  on  the  west. 
By  the  end  of  the  Palaeozoic  ^Eon  the  thickness  of  the  Palaeozoic 
sediments  was  a  thousand  feet  around  the  bases  of  the  Rocky 
Mountain  ranges ;  32,000  feet  in  the  Wahsatch  region,  and 
40,000  feet  at  the  extreme  western  Palaeozoic  limit  in  longitude 


HISTORICAL   GEOLOGY.  469 

117°  30'.  So  deeply  was  the  grand  Cordilleran  topography  of 
the  close  of  Eozoic  time  buried  from  observation. 

Similar  was  the  experience  of  the  ancient  Seaboard  Land. 
The  Appalachian  border,  which  sank  at  the  end  of  Eozoic  time, 
continued  to  sink  during  the  whole  of  Palaeozoic  time.  Sedi- 
ments accumulated  upon  it  to  the  depth  of  45,000  feet.  West- 
ward toward  the  modern  Mississippi  Valley,  they  diminish  to 
6,000  and  even  to  3,500  feet. 

Quite  the  reverse  was  the  movement  of  the  Laurentian  Land. 
Its  tendency  was  upward.  Some  additional  elevation  was  appar- 
ent at  the  end  of  each  succeeding  Age.  When  the  close  of 
Palaeozoic  time  was  approaching,  its  area  had  been  widened  so  as 
to  embrace  most  of  New  England,  New  York,  the  Upper  Penin- 
sula of  Michigan,  Wisconsin,  and  most  of  Minnesota.  Similar 
enlargement  was  experienced  along  its  other  borders. 

(2)  Progress  of  Animal  Organization.  While  these  great 
physical  transformations  were  in  progress,  parallel  transforma- 
tions and  parallel  progress  were  going  forward  in  the  organic  life 
of  the  planet.  Eozo5n  had  long  since  ceased  to  be  a  tenant  of 
the  ocean ;  but  its  great  works  were  lying  imperishable  beneath 
the  accumulating  masses  of  the  forming  continent.  As  soon  as 
the  tumult  of  the  closing  action  of  Eozoic  time  had  subsided,  the 
Palaeozoic  ocean  was  thronged  with  creatures  of  grades  compara- 
tively high — Trilobites,  Chambered  Molluscs,  Gasteropods,  and 
Brachiopods.  Coral  animals,  Crinoids,  Lamellibranchs  followed 
quickly,  geologically  speaking.  In  those  distant  ages  were  all 
the  experiences  which  characterize  life  of  our  own  times  —  hun- 
ger, fear,  pursuit  and  retreat,  slaughters  and  the  pangs  of  dying. 
The  very  attitudes  in  which  the  dead  were  buried  reveal  the 
shrinking  which  sentient  organization  experiences  when  the 
pains  of  dying  approach.  But  through  all  the  wide  ocean  no 
place  was  found  for  creatures  conformed  to  the  highest,  or  verte- 
brate, type  of  structure.  It  was  the  Reign  of  Invertebrates. 

As  the  land  extended  its  borders,  and  the  elements  became 
suited  to  the  requirements  of  higher  types  of  life,  there  were, 
first,  premonitions  of  the  advent  of  vertebrates,  and  then  the  on- 


470  GEOLOGICAL   STUDIES. 

coming  of  the  powerful  and  cruel  dynasty  of  armored  Fishes. 
They  ruled  during  the  later  Silurian,  the  Devonian,  and  the  Car- 
boniferous ages.  Until  the  last  period  of  the  Carboniferous,  ver- 
tebrate life  was  exclusively  aquatic,  and,  so  far  as  we  know, 
almost  exclusively  marine.  When  the  atmosphere  had  become 
respirable,  some  humble  Amphibian  forms  might  have  been  seen 
skulking  under  the  protection  of  the  flowerless  herbage  which 
had  sprung  up.  But  plated,  bony-scaled,  and  shark-like  fishes 
remained  the  dominant  vertebrates. 

(3)  The  Coal  Period.  The  last  period  of  the  Palaeozoic 
^Eon  was  marked  by  its  exuberance  of  vegetal  life.  Marine 
plants  had  existed  in  the  early  Laurentian.  Their  record  stands 
in  the  beds  of  graphite  which  were  then  formed,  and  the  deposits 
of  magnetite  and  haematite  which  are  believed  to  have  been  ac- 
cumulated through  organic  agency.  Scattered  land  plants  are 
thought  to  have  nourished  along  the  Silurian  and  even  the  Cam- 
brian shores,  since  some  obscure  driftwood  has  been  taken  from 
beds  of  the  Cincinnati  Group.  During  the  Devonian  ferns  and 
lepidodendroids  left  their  relics  ki  considerable  abundance;  but 
during  the  last  period  of  the  Palaeozoic  the  situation  became  pe- 
culiarly suited,  in  the  eastern  portions  of  North  America,  for  the 
development  of  an  extraordinary  volume  of  vegetation. 

The  sinking  of  the  Appalachian  geosynclinal  had  been  such 
that  the  Palasozoic  sediments  accumulated,  together,  perhaps, 
with  a  little  subsequent  elevation,  brought  the  sea  bottom  up  to 
the  sea  level,  or  a  little  above.  In  regions  farther  west  —  in 
Ohio,  Michigan,  Kentucky,  Indiana,  Illinois,  Iowa,  Missouri,  and 
eastern  Kansas — the  general  tenor  of  upheaval  begun  at  the  end 
of  Eozoic  time,  had  brought  the  sea  bottom  up  to  nearly  the  same 
level  as  it  reached  in  the  Appalachian  region.  Over  the  broad 
marsh  land,  which  thus  stretched  half  across  the  continent,  condi- 
tions uncommonly  favorable  for  vegetable  growth  existed.  The 
whole  expanse,  therefore,  became  clothed  with  a  general  type  of 
vegetation  in  correspondence  with  the  primitive  conditions  of  the 
world  —  mostly  ferns,  calamites,  sigillarians,  and  lepidodendroids. 

The  growth  and  prostration  of  this  vegetation  through  a  sue- 


HISTORICAL   GEOLOGY.  471 

cession  of  generations  resulted  in  a  bed  of  vegetable  material 
somewhat  peat-like  in  its  nature,  and,  like  peat,  preserved  from 
decay  by  saturation  in  water  and  exclusion  of  air.  Then  followed 
a  subsidence  of  the  whole  of  the  coal-making  area.  The  ocean 
returned,  and  sheets  of  fragmental  deposits  buried  the  vast  peat 
bog,  to  undergo  those  transformations  which  should  eventually 
bring  it  into  the  condition  of  bituminous  coal.  Another  uplift 
succeeded,  and  new  growths  covered  the  new  land.  Another  bed 
of  vegetable  matter  accumulated,  and  another  submergence  re- 
sulted in  its  burial  beneath  strata  of  sand  and  mud.  Thus  emerg- 
ences and  submergences  succeeded  each  other  during  the  entire 
coal-making  period.  It  is  not  supposed,  however,  that  all  these 
movements  were  synchronous  over  the  entire  coal-making  area. 
Undoubtedly,  some  portions  underwent,  at  times,  a  degree  of  sub- 
mergence, while  others  remained  above  sea  level.  The  emerg- 
ences, also,  must  have  been  experienced  sometimes  earlier  in  one 
part  of  the  area  than  in  others.  The  nonsynchronism  of  these 
movements  resulted  in  some  discontinuity  of  the  beds  of  coal, 
shale,  and  sandstone  thus  forming.  Hence  the  succession  of 
strata  in  Illinois  is  not  identical  with  the  succession  in  Ohio  and 
Pen  nsyl  vania. 

While  these  oscillations  of  level  were  in  progress  in  the  east- 
ern part  of  the  continent,  the  Cordilleran  region,  as  a  whole, 
remained  permanently  beneath  the  ocean.  The  ancient  island 
mountains  still  stood  emergent,  and  the  Nevadan  land  continued 
to  crumble,  in  furnishing  the  sediments  which  formed  the  last 
layers  of  the  Palaeozoic  mass. 

(4)  Close  of  the  falceozoic.  Great  geologic  events  were  now 
at  hand.  The  broad  coal-making  region  so  long  oscillating  up- 
ward and  downward,  as  if  under  the  stress  of  an  enormous  lateral 
pressure  from  which  it  was  seeking  relief,  at  length  yielded  to 
the  resistless  strain.  Huge  parallel  folds  of  the  crust  rose  along 
the  Appalachian  region.  A  mountain  chain  came  into  existence 
where  sea  bottom  had  been  during  all  the  Palaeozoic  time,  save 
the  period  of  bog  lands  while  the  coal  beds  had  formed.  The 
mountains  rose  to  altitudes  of  twelve  to  fifteen  thousand  feet. 


472  GEOLOGICAL   STUDIES. 

Before  human  eyes  rested  on  them  they  had  lost  by  erosion  half 
their  original  height.  The  disturbance  was  felt  as  far  as  eastern 
Kansas.  All  the  intervening  region  became  upland. 

There  is  reason  to  conclude  that  the  remnant  of  the  Seaboard 
Land  went  down  as  the  Appalachian  belt  came  up.  Thus  an  un- 
known amount  of  that  land  became  subsequently  concealed  by 
sediments  of  later  date.  The  Triassic  sandstones  of  Connecticut, 
New  Jersey,  and  seaboard  districts  farther  south  prove  that  im- 
mediately after  the  Appalachian  disturbance  the  border  was  con- 
siderably more  depressed  than  at  present,  and  the  Appalachian 
movement  may  probably  have  been  the  counterpart  of  this  de- 
pression. 

From  eastern  Kansas  westward  the  great  interior  ocean  re- 
mained undisturbed,  save  here  and  there  a  moderate  upward 
movement  revealed  in  the  broader  emergence  of  the  protruding 
granite  masses.  But  in  the  Wahsatch  region,  and  westward, 
enormous  alterations  of  level  took  place.  The  long  worn  Ne- 
vadan  Land  now  sunk  beneath  sea  level,  while,  reciprocally,  the 
sea  bottom  immediately  eastward,  as  far  as  the  Wahsatch,  and 
including  that  range,  rose  to  a  continental  emergence.  This  was 
now  the  western  continent,  lying  between  the  eastern  foot  of  the 
Wahsatch  and  western  Nevada,  in  longitude  117°  30'  —  the  re- 
gion now  known  as  the  "Basin  Province."  Between  the  new 
Basin  Continent  and  the  old  Nevadan  continent,  which  went  down 
there  was  a  complete  change  of  conditions.  The  continental  see- 
saw on  the  west  was  the  counterpart  of  the  continental  see-saw 
on  the  Atlantic  border.  The  mass  in  each  case  which  went  down 
was  on  the  side  of  the  ocean;  the  mass  which  came  up  was  next 
the  interior.  The  continental  masses  were  now  settled  for  another 
age  of  repose. 

3.  The  Mesozoic  ^Eon.  (1)  Continental  History.  East  of 
the  Great  Plains  the  land  was  now  extended  nearly  to  its  destined 
dimensions  (see  Fig.  353).  A  belt  along  the  Atlantic  was  still 
submerged,  and  also  a  broad  belt  on  the  Gulf  border.  The  latter 
sent  a  triangular  arm  of  the  sea  northward  to  Illinois,  and  wid- 
ened westward  into  an  ocean  which  stretched  over  the  central 


HISTORICAL   GEOLOGY.  473 

part  of  the  continent  as  far,  probably,  as  the  Arctic  Ocean.  Its 
eastern  border  was  in  Minnesota,  near  the  94th  meridian,  and  in 
Kansas,  near  the  96th.  Its  western  border  was  at  the  foot  of  the 
Wahsatch,  near  the  lllth  meridian.  It  stretched  continuously 
over  the  Great  Plains,  was  broken  into  an  archipelago  in  the 
Rocky  Mountain  belt,  and  was  diversified  with  a  few  island  emerg- 
ences, especially  northward,  across  the  intervening  distance  to 
the  Basin  continent.  North  and  south  this  Intercontinental  Sea 
reached  to  the  Gulf  and  the  Arctic  Ocean.  Over  this  area  Meso- 
zoic  sediments  were  spread.  They  rested  conformably  —  at  least 
in  the  40th  parallel  region  —  on  the  latest  Palaeozoic.  The  source 
of  the  materials  being  on  the  west,  the  thickest  accumulations 
were  in  that  direction.  Their  general  thickness  at  the  close  of 
the  Jurassic  Age  was  about  4,000  feet.  West  of  the  Basin  con- 
tinent was  another  ocean.  All  the  Nevadan  and  east  Californian 
part  of  it  had  resulted  from  the  post-Palaeozoic  subsidence  of 
land  which  had  stood  from  the  close  of  Eozoic  time.  The  sub- 
merged surface,  therefore,  was  deeply  eroded.  Over  this  the 
Mesozoic  sediments  were  now  deposited  unconformably.  They 
accumulated  to  a  depth  of  twenty  thousand  feet.  The  belt  along 
the  western  border  of  the  Basin  continent  was  destined  to  form 
the  Sierra  Nevada  mass.  Meantime  the  Appalachians  were  wast- 
ing, and  the  debris  were  strewn  along  the  contemporaneous  At- 
lantic and  Gulf  border,  from  Sandy  Hook  to  Georgia,  and  from 
Georgia  to  Texas. 

The  close  of  the  Jurassic  Age  was  now  at  hand.  It  was  sig- 
nalized, especially,  by  the  rise  of  the  vast  crumpled  folds  of  the 
Sierra  Nevada.  This  added  200  miles  to  the  westward  extension 
of  the  Basin  continent,  which  thus  became  the  Basin-Nevada 
continent.  It  stretched  southward  at  least  to  the  36th  parallel, 
and  probably  to  the  32d.  Northward  it  extended  into  Washing- 
ton Territory,  and  perhaps  to  the  Olympic  Mountains.  East  of 
the  Wahsatch,  however,  this  great  disturbance  was  not  felt,  save 
that  its  rock  fragments  and  finer  debris  were  sent  eastward  over 
the  ocean's  floor  as  far  as  Kansas.  These  coarse  materials  formed 


474  GEOLOGICAL   STUDIES. 

the  basal  or  Dakota  member  of  the  Cretaceous  System.  But  it 
was  laid  down  conformably  on  the  Jurassic. 

Along  the  Atlantic  border  the  Cretaceous  Age  was  marked 
by  a  moderate  depression.  The  ocean  encroached  farther  inland 
than  during  the  Jurassic.  The  Cretaceous  sediments,  accord- 
ingly, covered  and  concealed  nearly  all  the  Triassic  and  Jurassic. 
The  same  statement  applies,  also,  to  the  Gulf  border. 

The  close  of  the  Cretaceous  was  an  important  era  in  American 
geological  history.  To  this  epoch,  the  sedimentary  sheets  of  the 
central  region  east  of  the  Wahsatch  had  been  laid  down  in  con- 
formable superposition  from  the  beginning  of  the  Palaeozoic. 
Now,  however,  came  the  turn  of  the  region  at  present  known  as 
the  "Plateau  Province."  Upward  and  undulatory  movements 
were  experienced.  Now  rose  the  broad,  flat,  east  and  west  anti- 
clinal range,  known  as  the  Uinta  Mountains.  Not,  however,  by 
a  sudden  movement,  for  the  rise  was  prolonged  through  the 
whole  duration  of  the  resulting  land .  surf  ace,  and  proceeded 
slowly  enough  to  permit  the  drainage  streams  to  saw  chasms 
through  the  entire  height  of  the  mountain.  Eastward  of  the 
Uinta,  the  whole  continental  mass  was  raised;  and  this  brought 
with  it  the  Rocky  Mountain  ranges  to  a  higher  altitude.  The 
broad,  shallow  basin  of  the  Colorado  now  had  its  limits  marked 
out.  On  the. Pacific  Coast,  this  disturbance  was  felt  only  in  the 
defining  of  the  position  of  the  Coast  Ranges.  On  the  Atlantic 
and  Gulf,  the  continent  was  upraised;  and  a  belt  ranging  from 
fifty  to  a  hundred  miles  was  added  to  the  land. 

These  changes,  however,  were  not  accomplished  with  abrupt- 
ness. The  Cordilleran  sea  bottom  was  slowly  rising  during  the 
whole  Cretaceous  Age,  reaching  the  vicinity  of  sea  level  at  an 
earlier  epoch  on  the  Wahsatch  border  than  in  the  region  of  the 
Rocky  Mountains  and  Kansas.  Farther  south,  however,  in 
Texas,  the  Cretaceous  ocean  remained  a  deep  sea  till  the  close  of 
the  Age. 

The  great  feature  of  the  Cretaceous  and  post-Cretaceous 
.movements  was  the  reemergence  of  that  part  of  the  ancient  Cor- 
dilleran area  which  is  now  called  the  Plateau  Province,  though, 


HISTORICAL    GEOLOGY.  475 

indeed,  extensive  inland  lakes  continued  through  the  next  aeon. 
The  two  limbs  of  the  American  continent  were  now  joined 
together.  From  middle  California  to  Boston  Bay  was  a  contin- 
uous land  connection.  Only  a  narrow  border  remained  to  be 
added  around  the  Atlantic,  Pacific,  and  Gulf  coasts,  and  North 
America  would  be  complete. 

(2)  Progress  of  Mesozoic  Life.  Vegetable  organization 
reached,  in  the  early  Mesozoic,  the  grade  of  Cycads  and  Conifers. 
Tree  Ferns  were  still  abundant.  In  the  later  Mesozoic,  angio- 
sperms  and  palms  were  common.  The  marsh  borders  of  the 
emerging  lands  of  the  Dakota  period  have  preserved  a  great 
abundance  of  the  leaves  of  plants  belonging  to  modern  and 
closely  related  genera.  Lesquereux,  in  a  recent  publication, 
enumerates  from  the  Dakota  Cretaceous  91  species  of  flowering 
plants,  belonging  to  29  living  genera.  These  include  4  species  of 
Sequoia,  7  of  Oak,  5  of  Willow,  5  of  Poplar,  5  of  Plane  Tree,  7 
of  Fig,  4  of  Magnolia,  8  of  Tulip  Tree,  9  of  Sassafras,  8  of  Sar- 
saparilla.  Evidently  the  forest-covered  land  presented,  in  the 
early  Cretaceous,  a  decidedly  modern  aspect.  American  Creta- 
ceous vegetation  was,  in  fact,  more  advanced  than  that  of  Europe. 
In  the  Laramie,  or  closing  period,  it  had,  according  to  Lesque- 
reux, an  Eocene,  or  even  a  Miocene,  aspect.  That  is,  the  nearest 
European  analogues  of  Laramie  species  occur  in  the  Eocene 
rather  than  in  the  Cretaceous.  At  the  same  time,  the  reptilian 
and  molluscan  species  of  the  Laramie  are  indisputably  Creta- 
ceous; and  these  are  best  suited  to 'determine  the  age  of  a  for- 
mation. Sir  W.  Dawson,  in  a  very  recent  note  (1885),  records 
the  occurrence  of  Brasenice  antiqua  in  beds  of  the  Belly  River 
series,  in  the  Canadian  Northwest.  This  species  is  scarcely  dis- 
tinguishable from  the  modern  Brasenice  (Hydropeltis)  purpurea, 
though  it  occurs  in  strata  older  than  those  affording  remains  of 
Diclonius,  a  Cretaceous  Dinosaur.  The  horizon  is  probably 
Lararnie. 

Among  Polyp  corals,  the  ancient  type  of  Tetracoralla,  having 
the  parts  in  multiples  of  four,  were  mostly  extinct,  and  modern 
Hexacoralla  had  taken  their  place.  The  type  of  Crinoids,  which 


476  GEOLOGICAL   STUDIES. 

had  culminated  in  the  earlier  Carboniferous,  was  now  declining, 
and  the  higher  Starfishes  and  Echinoids  were  succeeding.  The 
old  spire-bearing  Brachiopods,  as  also  the  Orthids  and  Stropho- 
me'noids,  and  other  types,  had  dropped  out  of  existence;  and 
Terebratuloids  were  now  in  the  ascendent.  The  waters  swarmed, 
however,  with  Lamellibranchs  and  Gasteropods.  The  higher 
molluscs  were  richly  represented  by  Ammonites  and  Belemnites. 
But  the  former  showed,  toward  the  close  of  the  Cretaceous,  a 
marked  decline.  Ganoid  and  Selachian  fishes  continued  in  abun- 
dance; but  the  former  early  dispensed  with  the  vertebrated  tail. 
This  is  an  embryonic  character,  and  accordingly  belonged  to  the 
early  stages  of  type  development.  The  reptiles  were  the  great 
feature  of  the  life  of  the  JEon.  Their  modes  of  life  and  diversi- 
fication of  type  have  been  elsewhere  described.  Their  graduation 
into  the  type  of  birds  presents  facts  full  of  curious  and  philo- 
sophic interest.  Perhaps  the  most  significant  event  was  the  advent 
of  Mammals;  since  this  brought  organization  up  to  the  class- 
grade  of  man,  and  constituted  a  final  renewal  of  the  promise  of 
man's  ultimate  advent.  The  first  mammals  dwelt  on  the  Triassic 
land,  and  were  feeble  and  inconspicuous.  In  the  Jurassic  Age, 
they  were  still  feeble,  but  somewhat  more  numerous.  In  the 
Cretaceous  they  seem  to  have  gained  nothing  in  bulk,  power,  or 
importance.  Evidently,  the  appropriate  age  for  the  unfolding  of 
the  Mammalian  type  had  not  yet  arrived. 

4.  The  Ccenozoic  ^Eon.  (1)  The  Tertiary  Age.  It  will  be 
remembered  that  Mesozoic  time  was  concluded  by  an  uplift  of 
the  whole  Cordilleran  region,  and  the  extinction  of  the  great 
Plateau  or  mediterranean  sea.  But  in  the  basin  of  the  Colorado 
River,  a  great  depression  remained  without  complete  drainage  to 
the  sea.  There  rested,  during  the  Eocene,  a  great  Eocene  Lake, 
extending  from  the  upper  waters  of  the  Yellowstone  to  New 
Mexico.  This,  at  first  salt,  became  brackish,  and,  at  length,  a 
lake  of  fresh  water.  The  sediments  accumulated  in  it  during  the 
the  first  epoch  constitute  the  Wahsatch  formation  (=Vermillion 
Creek  Group,  King;  =  Bitter  Creek  Group,  Powell).  In  the 
progress  of  time  occurred  three  successive  orographic  disturb- 


HISTORICAL   GEOLOGY. 


477 


ances.  The  first,  during  the  progress  of  the  Wahsatch,  contracted 
the  great  lake  on  the  north  and  south.  It  stretched  now  from 
the  valley  of  the  Green  River  north  and  south  of  the  Uinta 
Mountains,  and  perhaps,  also,  to  the  west  of  the  Wahsatch 
Range,  in  Utah  and  Nevada.  In  it  were  deposited  the  sediments 
forming  the  Green  River  division  of  the  Wahsatch  formation 
(=  Elk  Group,  King). 


FIG.  366.— NORTH  AMERICA,  NEAR  THE  BEGINNING  OF  C^ENOZOIC  TIME. 

The  second  disturbance  terminated  the  Wahsatch  epoch. 
The  great  Eocene  Lake  was  now  further  contracted.  It  con- 
sisted, during  this  epoch,  of  two  or  more  divisions.  One  of  these 
rested  in  the  Green  River  basin  north  of  the  Uinta  Mountains; 
another,  the  Washakie  basin,  lay  east  of  the  Green  River,  and  a 
third  was  in  western  Colorado.  The  deposits  collected  formed 
the  Bridger  Group. 

The  third  disturbance  restricted  the  Eocene  Lake  to  the 
region  east  and  south  of  the  Uinta  Mountains,  in  the  valley  of 
the  Green  and  White  rivers.  In  it  was  deposited  the  uppermost 


478  GEOLOGICAL    STUDIES. 

of  the  Eocene  formations  —  the  Uinta  (=  Brown's  Creek  Group, 
Powell).  During  these  events  the  province  of  the  Great  Plains 
appears  to  have  been  partly  dry  land. 

The  next  orographic  movement  terminated  the  Eocene.  The 
Great  Plains  were  now  depressed,  and  a  lake  stretched  from  the 
Missouri  River  to  eastern  Wyoming,  Colorado,  and  the  Wind 
River  Valley,  and  from  northern  Kansas  far  into  British  America. 
A  long,  narrow  depression  took  place,  also,  in  the  far  West, 
along  the  eastern  base  of  the  Cascade  Range  and  Sierra  Nevada. 
It  stretched  from  Washington  Territory  through  Oregon,  Nevada, 
and  California.  The  deposits  in  the  western  lake  were  chiefly 
the  tuffs  and  rearranged  ejecta  of  volcanic  eruption,  and  attained 
a  thickness  of  4,000  feet.  The  deposits  in  the  eastern  lake  were 
the  simple  detritus  from  surrounding  lands,  and  attained  a  thick- 
ness of  150  feet  in  Nebraska,  300  feet  in  Colorado,  and  2,000  feet 
in  the  Uinta  Mountains.  The  western  is  the  Truckee  formation 
(—  John  Day  Group,  King);  the  eastern,  the  White  River  forma- 
tion; but  some  uncertainty  remains  as  to  their  precise  synchro- 
nism. Along1  the  Pacific  slope,  deposits  accumulated  to  the  depth 
of  four  or  five  thousand  feet  in  California  and  Oregon,  which, 
with  the  closing  disturbance,  were  upraised  in  the  Coast  Ranges. 

This  disturbance  changed  again  the  bounds  of  the  interior 
lakes,  and  inaugurated  the  Pliocene  epoch.  The  whole  interior 
seems  to  have  experienced  a  general  depression,  which  interrupted 
the  drainage  to  the  sea.  The  western  Miocene  beds  were  thrown 
into  folds.  The  resulting  lake  was  divided  in  two  by  the  archi- 
pelago of  the  Rocky  Mountains.  We  find  the  deposits  of  the 
Pliocene  or  Loup  River  beds  at  many  points  between  the  Sierra 
Nevada  and  the  eastern  limit  of  the  Great  Plains,  and  from  Ore- 
gon to  New  Mexico.  They  reach  into  Kansas  and  stretch  north- 
ward, occupying  the  valleys  of  the  Rocky  Mountains.  They 
embrace  the  Niobrara  Group,  King  and  Marsh  +  Humboldt  Group, 
King  +  North  Park  Group,  Hague  and  Hayden.  The  Pliocene 
beds  of  the  Great  Plains  rest  conformably  on  the  Miocene,  or,  in 
some  regions,  on  the  Cretaceous,  and  attain  a  thickness  of  2,000 
feet.  Those  of  the  Basin  and  Plateau  provinces  rest  uncon- 


HISTORICAL   GEOLOGY.  479 

formably  on  the  Miocene,  and  are  not  over  1,000  feet  thick.  After 
the  shrinkage  of  the  Loup  River  lakes,  deposition  continued,  form- 
ing1 the  so  called  Equus  Beds  or  Upper  Pliocene  (sometimes  also 
regarded  as  post-Pliocene)  occurring  in  Oregon,  California,  and 
Nevada;  and  in  the  eastern  United  States,  in  cavern  and  clay 
deposits  along  the  Delaware  and  Potomac  rivers. 

The  movement  which  inaugurated  the  Pliocene  appears  to 
have  resulted  in  an  elevation  of  the  Atlantic  seaboard  north  of 
South  Carolina.  During  the  Pliocene,  probably  the  submerged 
shore  land  off  the  present  coast  marked  the  border  of  the  land. 
During  the  Pliocene,  also,  the  submerged  Hudson  gorge  was 
principally  elevated  (Fig.  358).  Throughout  the  Tertiary  the 
Atlantic  and  Gulf  coasts  experienced  a  slow  and  mostly  progres- 
sive upheaval.  But  the  most  considerable  emergence  on  the  Gulf 
and  South  Atlantic  was  at  the  end  of  the  Eocene,  and  along  the 
North  Atlantic,  after  the  Miocene. 

The  continental  oscillations  sketched  in  the  foregoing  para- 
graphs are  graphically  represented  in  the  accompanying  aeonic 
sections,  Fig.  367.  The  sections  are  mere  diagrams,  representing 
uplifts  and  subsidences;  but  they  will  greatly  aid  the  memory 
and  imagination  in  retaining  a  vivid  conception  of  the  locality 
and  order  of  succession  of  each  of  those  great  orographic  move- 
ments which  have  made  American  geology  what  it  is,  and  have 
shaped  the  face  of  the  continent  in  those  forms  destined  to  char- 
acterize it  through  the  age  of  human  occupation. 

(2)  The  Glacial  Epoch.  During  the  later  Tertiary  moderate 
elevations  occurred  in  various  regions,  completing  the  drainage 
of  the  land,  and  establishing  a  tenor  of  events  destined  to  con- 
tinue to  such  extent  as  to  determine  the  advent  of  another  epoch. 
The  continuance  of  the  elevation  became  general  over  the  north- 
ern part  of  the  continent,  and  more  especially  the  northeastern. 
The  climate,  therefore,  which  had  been  milder  than  our  present 
climate,  experienced  an  increase  of  winter  severity,  and  a  pro- 
longation of  the  snowy  season.  The  higher  elevation  of  the  land 
increased  the  corrasive  action  of  the  streams  and  deepened  their 
channels.  It  also  produced  an  extension  of  the  land  along  the 


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FIG.  3G7-— ^EONIC  SECTIONS  ACKOSS  THE  CONTINENT  ALONG  THE  FORTIETH  PARALLEL. 
[East  of  the  8?d  meridian  the  Sections  follow  the  38th  Parallel.]  Compare  with 
^Eonic  Maps,  Figs.  297,  304,  312,  340,  353,  354,  and  356. 


HISTORICAL   GEOLOGY.  481 

sea  border.  It  is  probable  that  the  border  of  the  steep  basin 
slope  of  the  Atlantic,  before  mentioned,  marks  the  position  of 
the  ancient  shore  in  post-Pliocene,  if  not  in  Pliocene,  time. 
This,  however,  could  not  have  formed  the  continental  border 
along  the  South  Atlantic  during  Pliocene  time,  since  in  South 
Carolina,  Pliocene  deposits  prove  Pliocene  submergence.  In 
early  post-Pliocene  time,  Long  Island  was  150  miles  broad,  and 
the  western  part  of  Long  Island  Sound  was  the  lower  valley  of 
the  Connecticut  River.  The  Hudson  River  still  pursued  its 
course  between  high  banks,  135  miles  beyond  New  York.  This 
supposes  the  post-Pliocene  elevation  of  the  land  to  have  been 
equal  to  the  highest  attained. 

With  progressive  northern  elevation,  the  rigor  of  the  climate 
increased.  The  northern  zone  of  perpetual  snow  widened  to 
temperate  latitudes.  Under  the  influence  of  the  summer  sun,  the 
broad  snow  mass,  though  not  dissipated,  was  reduced  to  the  con- 
dition of  glacier  ice.  The  snows  had  fallen  over  the  landscape, 
and  bedded  themselves  about  the  trees  of  the  forest.  They  had 
gathered  themselves  about  all  the  rocky  saliences,  and  filled  the 
rugged  gorges  worn  by  the  long  corrading  streams.  When, 
therefore,  the  pervading  glacier  moved,  as  all  glaciers  must 
move,  the  forests  were  prostrated,  and  the  rocky  crags  were 
wrenched  from  their  fastenings.  The  angular  fragments  were 
frozen  in  the  glacier's  bottom,  and  like  diamonds  in  their  setting, 
they  scored  the  underlying  surface.  That  surface  was  covered 
with  sands  and  clays  and  rock  fragments,  the  result  of  the  rock 
disintegration  of  hundreds  of  thousands  of  years.  This  inco- 
herent material  was  moved  and  mixed  by  the  glacier.  With  it 
were  mingled  the  shattered  remnants  of  the  forest.  By  it  the 
old  gorges  and  gullies  and  river  valleys  were  filled.  These  debris 
of  former  ages  were  swept  clean  from  the  solid  surface  of  the 
rocks;  and  the  moving  glacier  mass  scoured  and  scored  the  solid 
rocks.  It  slid  over  moderate  elevations,  and  crossed  many  of  the 
valleys  which  intercepted  its  course.  Eastward,  it  travelled  over 
Long  Island,  and  out  to  the  ancient  shore.  In  Ohio  it  reached 
the  Ohio  River.  Farther  west,  its  limit  was  reached  in  latitudes 


482  GEOLOGICAL   STUDIES. 

considerably  higher.  It  will  be  understood  that  the  southern 
glacier  limit  was  coincident  with  the  southern  limit  of  the  Drift, 
as  shown  on  the  map,  Fig.  356. 

The  course  of  the  continental  glacier  was  not  independent  of 
the  larger  topographic  features  of  the  land.  It  tended  to  move 
downward  from  all  elevations.  The  courses  of  the  great  valleys 
determined  deflections  sometimes  for  a  hundred  miles  or  more. 
It  followed  up  the  valley  of  the  St.  Lawrrence.  It  continued 
along  the  axis  of  Lake  Erie,  and  up  the  valley  of  the  Maumee; 
but  it  will  be  remembered  that  the  slopes  were  different,  some- 
times reversed  by  the  northern  elevation  of  the  epoch.  The  gla- 
cier filled  the  valley  of  the  Connecticut  with  a  broad  ice  river. 
It  flowed  down  the  valleys  of  the  Mohawk  and  the  Hudson. 
Pursuing  its  way  along  the  channel  now  submerged,  it  excavated 
the  great  fiord  which  lies  now  over  a  hundred  miles  at  sea,  and 
sunken  in  500  feet  of  water.  It  accumulated  to  a  depth  of,  per- 
haps, 5,000  feet.  At  this  depth  the  heat  from  the  earth's  interior 
would  be  sufficient  to  melt  the  glacier  beneath  as  rapidly  as  any 
probable  growth  above.  The  sub-glacial  melting  created  copious 
sub-glacial  streams,  which  transported  detrital  material,  and  con- 
tributed much  to  the  observed  arrangements  of  the  Drift. 

In  regions  beyond  the  limits  of  the  continental  glacier,  local 
glaciers  gathered  on  mountain  summits  and  slopes,  and  coursed 
down  the  mountain  valleys,  as  modern  glaciers  move  in  Alpine 
valleys.  Such  mountain  glaciers  clothed  the  higher  slopes  of 
the  Appalachians,  the  Rocky  Mountains,  the  Sierra  Nevada,  and 
most  other  ranges  farther  north.  The  remnants  of  some  of  these 
local  glaciers  survive  to  our  times.  (See  especially  the  Memoir 
of  I.  C.  Russell.)  Even  the  modern  Alpine  glaciers  are  but  ves- 
tiges of  a  wide  general  glaciation.  Under  such  a  sheet  of  ice 
lay,  for  probably  thousands  of  years,  the  fair  continent  which  in 
geologically  recent  times  had  been  clothed  with  a  forest  which 
gave  it  an  aspect  exceedingly  like  that  of  a  modern  landscape. 
The  desolate  surface  of  glacier-clad  Greenland  remains  a  vivid 
picture  of  northeastern  North  America  only  a  few  thousand  years 
ago. 


HISTORICAL   GEOLOGY.  483 

It  is  not  necessary  to  suppose  the  climate  was  characterized 
by  excessive  cold.  Moisture  and  precipitation  are  necessary. 
Where  these  are  abundant,  the  snow  accumulation  may  outlast  a 
summer  of  high  temperature.  The  glaciers  of  the  Alps  descend 
to  the  borders  of  the  fields  where  crops  of  grass  and  potatoes 
grow.  The  snow  in  Tuckerman's  ravine,  in  the  White  Mount- 
ains, lasts  till  August,  because  it  is  abundant.  In  the  same 
climate  the  general  accumulation  of  snow  might  be  sufficient  to 
last  till  snow  falls  again.  With  the  surface  widely  covered,  the 
temperature  could  not  rise  much  above  32°  Fahr.,  and  less  snow 
would  then  suffice  to  withstand  the  whole  summer  heat.  The 
continental  glacier  existed  in  the  eastern  United  States,  where 
precipitation  is  now  greatest.  It  was  wanting  over  the  Great 
Plains  and  the  Northwest,  where  precipitation  is  still  scanty. 

(3)  The  Champlain  Epoch.  The  epoch  of  elevation  and 
cold  was  followed  by  one  of  subsidence  and  warmth.  From  its 
extreme  limit  the  continental  glacier  began  to  retreat.  There 
must  have  been  left  originally  a  terminal  moraine  of  great  mag- 
nitude. The  melting  of  the  ice  across  half  the  breadth  of  the 
continent  resulted  in  floods,  which  swept  southward,  carrying  the 
incoherent  products  of  glaciation,  and  depositing  them  in  the 
state  of  confused  stratification  which  we  see  in  the  Modified 
Drift.  To  what  extent  the  retreat  continued  we  have  no  means 
of  learning.  It  appears,  however,  that  some  portions  of  the  un- 
covered surface,  as  over  central  Illinois,  had  time  to  develop  a 
considerable  amount  of  vegetation  and  form  a  soil. 

Then  followed  a  return  of  cold,  and  the  glacier  again  ad- 
vanced. It  does  not  appear  that  the  second  advance  was  equal 
to  the  first.  On  the  final  retreat  the  great  terminal  moraine 
was  left,  which  has  been  traced  so  continuously  across  the  coun- 
try, and  mapped  in  Fig.  356.  The  return  of  another  geolog- 
ical springtime  gave  birth  to  renewed  floods,  which  continued 
the  work  begun  at  the  time  of  the  previous  thaw.  These  new 
floods  swept  over  the  old  moraine,  and  probably  scattered  and 
levelled  to  a  large  extent  the  accumulation  of  materials.  This 
may  explain  the  less  conspicuous  character  of  this  moraine, 


484  GEOLOGICAL   STUDIES. 

though  formed  through  the  action  of  the  severest  cold  and  the 
most  extended  glacier.  The  glacial  flood  sought,  of  course,  the 
valleys  of  the  great  streams  for  its  main  outlet  to  the  sea, 
and  thus  bore  far  southward  large  quantities  of  driftwood,  and 
even  ice  rafts  with  loads  of  sand  and  bowlders.  But  the  flood 
swept  also  over  the  general  surface  of  the  land;  and  thus  the 
states  not  reached  by  the  action  of  the  ice  were  reached  and 
benefited  by  the  action  of  the  flood  which  sprang  from  the  ice. 

It  is  to  be  remarked  that  the  aggregate  action  of  the  Glacial 
and  Champlain  epochs  was  directly  ameliorative,  and  may  be  re- 
garded as  a  preparation  for  the  needs  of  the  new  fauna  and  flora 
which  were  destined  to  appear.  As  a  general  principle,  it  may 
be  asserted  that  each  renewed  terrestrial  surface  in  the  whole 
history  of  life  has  been  exhausted  in  supplying  the  needs  of  the 
population  introduced  to  occupy  it.  The  present  terrestrial  sur- 
face is  visibly  deteriorating.  The  pre-glacial  surface  had  been 
wasted  and  scored  by  the  erosions  of  the  ^Eon  which  supplied  the 
demands  of  Pliocene  populations.  By  glacier  action  the  old  scars 
were  removed  —  the  gaping  gorges  were  filled;  the  rock  materials 
disintegrated  through  ages  were  stirred  to  the  bed  rock,  and  dis- 
tributed in  a  continuous  sheet ;  new  materials  originated  from 
glacial  wear;  and  when  the  floods  came,  a  beneficent  assortment 
left  the  finer  products  at  the  surface,  and  extended  the  reparative 
action  over  several  degrees  of  latitude  southward.  The  final 
result  was  a  land  surface  specially  suited  to  the  needs  of  an 
industrial  and  civilized  race  of  men. 

The  course  of  things  thus  in  progress  continued  until  the 
northward  subsidence  carried  the  land  far  below  its  pre-glacial 
level,  and  even  below  its  present  level.  The  consequence  was  an 
encroachment  of  the  sea  on  the  land.  The  records  of  beach 
action  still  remain  at  various  altitudes  above  present  sea  level, 
showing  the  greatest  Champlain  depression  northward.  It  thus 
appears  that  southern  New  England  sank  10  to  25  feet  below  its 
present  level;  Sancati  Head  on  Nantucket,  85  feet;  parts  of  the 
coast  region  of  Maine,  217  feet;  the  borders  of  Lake  Champlain, 
350  to  400  feet;  the  region  of  Montreal,  nearly  500  feet;  that  of 


HISTORICAL   GEOLOGY.  485 

the  Bay  of  Fundy,  350  to  400  feet;  the  Labrador  coast,  400  to 
500  feet;  parts  of  the  Arctic  regions,  over  1,000  feet.  On  Ben- 
nett Island  De  Long  found  beach  deposits  at  the  height  of  100 
feet.  Marine  shells  were  found  1,000  feet  above  the  Arctic  level; 
bnt  it  does  not  appear  that  they  were  not  Pliocene  or  Miocene. 
Whether  this  subsidence  was  felt  by  the  interior  of  the  continent 
it  is  impossible  to  state.  The  Pliocene  of  the  Great  Plains  re- 
mains from  4,000  to  7,000  feet  above  sea  level;  and  the  fact  ren- 
ders questionable  any  higher  Quaternary  elevation  or  any  Cham- 
plain  subsidence. 

The  subsidence  of  the  land  caused  a  reversal  of  a  portion  of 
the  drainage  of  the  Northern  States.  While  the  North  was  ele- 
vated, Winnipeg  Lake,  then  greatly  increased  in  dimensions,  was 
drained  into  the  Missouri.  It  has  even  been  suggested  that  a 
large  stream  flowed  southward  through  the  present  valley  of  the 
Minnesota.  The  great  lakes  also  found  various  outlets  toward 
the  south.  With  subsidence  of  the  land  some  of  these  courses 
became  obstructed,  and  others  even  reversed. 

(4)  Effects  of  Glacier  Pressure.  In  thus  delineating  the 
events  of  the  Quaternary  Age,  I  have  followed  the  accepted 
teaching.  But  I  think  it  may  be  useful  to  suggest  some  conse- 
quences of  glacier  pressure  over  the  northern  and  eastern  parts 
of  the  continent,  which  may  necessitate  some  modifications  of 
accepted  views.  If,  as  is  now  commonly  held,  the  accumulation 
of  marine  sediments  may  suffice  to  depress  the  earth's  crust  under 
the  sea,  assuredly  the  accumulation  of  5,000  feet  of  ice  upon  the 
land,  over  half  the  area  of  a  continent,  would  cause  a  depres- 
sion of  the  terrestrial  crust  —  such  as  glaciated  Greenland,  for 
instance,  is  actually  undergoing.  Croll,  assuming  the  crust  to 
remain  rigid  under  such  a  pressure,  has  discussed  the  necessary 
shifting  of  the  earth's  centre  of  gravity,  and  consequent  flooding 
of  northern  regions.  But  the  same  flooding  would  ensue  without 
a  shifting  of  the  centre  of  gravity,  if  the  crust  were  depressed. 
If  then  the  northern  subsidence  and  submergence  noted  were 
coincident  with  glaciation,  instead  of  subsequent,  the  phenomena 
resulting  would  be  precisely  such  as  we  observe.  The  glacier 


486  GEOLOGICAL   STUDIES. 

would  not  persist  along  shores  buried  by  the  sea.  The  same  sea 
bottom  would  be  there  as  if  the  glacier  had  disappeared  from  all 
the  land.  So  the  submergence  seems  to  have  been  coeval  with 
glaciation  rather  than  subsequent. 

Again,  a  sub-glacial  depression  over  the  north  and  east  of  the 
continent  must  have  reacted  beneath  the  crust  in  other  regions  — 
and  especially  in  regions  bordered  by  the  depression,  and  most 
especially  if  bordered  on  the  east  as  well  as  the  north.  The  last 
was  the  situation  of  temperate  North  America  west  of  the  Rocky 
Mountains.  Now  the  evidence  is  that  the  Plateau  and  Basin 
Provinces  have  suffered  from  powerful  vertical  actions.  That 
enormous  outflows  of  lava  have  occurred  is  another  striking  fact. 
These  occurrences  have  been  generally  synchronized  with  the 
close  of  the  Pliocene  Epoch;  but  here  are  grounds  for  assuming 
them  to  have  been  coincident  with  the  great  submergence  at  the 
east. 

(5)  The  Recent  Epoch.  The  rise  of  the  land  from  its  deep 
submergence  to  its  present  general  altitude  marks  the  beginning 
of  the  Recent  Epoch.  As  the  land  did  not  return  to  its  former 
elevation,  a  wide  belt  along  the  Atlantic  shore  northward  remains 
submerged.  In  the  interior  the  descent  of  the  streams  is  less 
than  formerly.  Hence  their  rate  of  flow  is  less,  and  their  ancient 
channels  remain  partly  filled  with  Drift  deposits.  Most  of  the 
larger  streams  now  flow  many  feet  above  their  ancient  beds. 

When  the  present  level  of  the  land  was  assumed,  the  water 
of  Lakes  Erie,  Huron,  and  Michigan  stood  many  feet  above  the 
present  level.  This  was  probably  due,  as  has  been  explained,  to 
an  obstruction  then  existing  at  the  escarpment  over  which,  near 
Lewiston,  the  drainage  of  these  lakes  had  to  pass.  During  this 
period  of  high  water  the  so  called  "  Erie  clays  "  were  deposited 
which  we  now  see  along  the  borders  of  these  lakes.  The  simul- 
taneous high  floods  of  the  rivers,  which  left  their  terraces  at  vari- 
ous high  elevations,  were  due,  perhaps,  to  the  prolonged  melting 
of  the  ice,  and  partly,  perhaps,  to  a  continuance,  at  moderated 
temperatures,  of  that  copious  precipitation  which  at  snowy  tem- 
peratures had  been  the  essential  condition  of  glacier  formation. 


HISTORICAL   GEOLOGY.  487 

Thus  there  may  have  been  a  pluvial  epoch,  beginning  during  the 
progress  of  the  Champlain  moderation  of  climate,  and  extending 
down  into  recent  times.  The  diminution  of  precipitation  which 
then  followed  appears  to  be  continuing  into  the  present. 

The  subsidence  of  the  floods  left  innumerable  small  lakes 
scattered  over  surfaces  having  but  little  slope.  The  peculiar 
kettle-like  configuration  of  parts  of  the  surface,  especially  along 
the  morainic  belts,  favored  the  retention  of  small  bodies  of  water. 
With  the  lapse  of  time,  drainage  outlets  have  been  worn  for  some 
of  these,  and  others  have  been  completely  filled  with  deposits  of 
marl  and  peat. 

In  the  present  epoch,  the  land  has  the  appearance  of  stability, 
except  as  occasionally  affected  by  momentary  earthquake  move- 
ments. In  truth,  however,  many  shores  are  undergoing  slow 
elevation  or  depression.  These  are  movements  which,  in  centu- 
ries, or  at  least  in  geological  periods,  may  amount  to  changes  of 
level  as  great  as  any  which  geological  research  has  brought  to 
light.  The  coast  of  New  Jersey,  for  instance,  is  represented  by 
Professor  Cook  as  subsiding  at  the  rate  of  two  feet  in  a  hundred 
years.  At  Uddevalla,  in  Sweden,  the  coast  is  rising  above  the 
Baltic  level  at  the  rate  of  four  feet  in  a  century;  and  north  of 
that,  the  rise  is  more  rapid.  Along  six  hundred  miles  of  the 
coast  of  Greenland,  a  slow  subsidence  is  taking  place.  Numerous 
facts  of  this  kind  are  known. 

When  the  rivers  were  at  flood  on  the  continent  of  Europe, 
man  was  there.  He  was  present,  apparently,  during  an  earlier, 
interglacial  epoch.  In  America,  he  found  a  home  during  the 
same  epoch,  as  far  north  as  New  Jersey,  and,  in  unglaciated  Cal- 
ifornia, he  left  his  bones  buried  in  the  gravels  which  underlie 
great  lava  sheets  poured  out  in  early  Quaternary,  or  late  Pliocene 
times.  That  man  existed  in  remote  preglacial  times  is  not  im- 
probable; but  he  was  represented  by  an  inferior  race,  and  lived  in 
some  congenial  climate.  The  men  who  pressed  upon  the  borders  of 
the  retreating  ice  were  hardy  adventurers,  who  had  already  come 
into  the  possession  of  the  arts  needed  to  secure  comforts  under 
trying  climatic  conditions. 


488  GEOLOGICAL   STUDIES. 

But,  in  any  view  of  the  epoch  of  human  origin,  man  stands  as 
the  crowning  and  consummated  event  in  a  series  of  intelligible 
preparations  and  promises  which  extend  back  through  vast  inter- 
vals of  time  to  Eozoon  and  the  primeval  ocean. 

§  3.     Ulterior  History. 

We  need  not  remain  in  complete  ignorance  of  that  part  of 
the  world's  appointed  history  which  is  yet  future.  It  is  scarcely 
true  that  we  cannot  be  certain  of  any  event  which  yet  lacks  real- 
ization. But,  if  it  were  true,  there  are  impending  events  so 
nearly  certain  that,  like  to-morrow's  sunrise,  their  failure  can  be 
determined  by  nothing  -less  than  a  suspension  of  the  order  of 
nature  as  known  to  us;  and  knowledge,  within  the  limitations  of 
the  recognized  order  of  nature,  cannot  be  pronounced  destitute 
of  value. 

Certain  activities,  like  the  return  of  summer,  and  the  occur- 
rence of  eclipses,  proceed  under  the  laws  of  matter  which,  to  our 
cognizance,  may  be  regarded  as  fixed  and  invariable.  Others 
proceed  in  accordance  with  methods,  or  laws,  made  known  to  us 
through  adequate  observation  and  inference;  and  these  furnish 
us  grounds  of  anticipation  scarcely  less  solid  than  the  others. 

We  know,  for  instance,  that  if  the  earth  continues  its  orbital 
and  rotary  motions  without  great  change  in  the  inclination  of  its 
axis;  if  the  sun  retains  its  efficiency,  and  all  other  conditions 
determining  the  present  order  of  nature  remain  undisturbed,  the 
seasons  will  continue  to  recur;  evaporation  and  precipitation, 
freezing  and  thawing,  will  continue  for  a  thousand  or  a  million 
years  to  come,  as  they  have  continued  through  the  past.  If  the 
principle  of  gravitation  remains  undisturbed,  and  the  solvent  and 
mechanical  actions  of  moving  water  remain  as  now,  it  is  certain 
that  processes  of  aqueous  erosion  will  continue  to  wear  away  the 
materials  of  the  earth's  crust;  and  the  processes  of  sedimentation 
will  continue  to  fill  the  undrained  depressions  of  the  earth's 
surface. 

Thus,  we  may  be  satisfied  that  the  Niagara  gorge  will  be  con- 
tinued; and,  if  we  use,  as  a  rule,  the  slopes  of  the  gorge  already 


HISTORICAL   GEOLOGY.  489 

excavated,  we  may  conclude  that  in  the  distant  future,  the  bot- 
tom of  the  gorge  will  pierce  the  bottom  of  Lake  Erie,  and  thus 
that  lake  will  be  gradually  drained,  and  become  a  river.  We 
may  further  reason  that  since  lakes  Huron  and  Michigan  stand 
at  nearly  the  same  level  as  Lake  Erie,  these  will  be  lowered  as 
much  as  the  latter;  and  because  their  depths  exceed  that  of 
Lake  Erie,  there  will  result  two  or  more  small  lakes,  connected 
by  a  river,  which  will  flow  along  the  drained  basin  of  Lake  Erie, 
and  down  the  steep,  unnavigable  slope,  continuing  through  the 
Niagara  gorge  to  Lake  Ontario. 

We  may  reason  similarly  about  the  general  wear  and  wastage 
of  the  land.  It  has  been  estimated,  from  observation,  that  the 
surface  of  North  America  is  lowered  by  denudation  about  one 
foot  in  four  thousand  years.  This  determination  immediately 
suggests  that  the  land  is  destined  to  undergo  final  wastage.  As 
the  detritus  finds  its  way  into  the  sea,  the  latter  is  slowly  filling 
up,  and  the  sea  bottom  will  continually  approach  the  level  of  the 
land.  Unless  the  supply  of  surface  water  fails,  the  sea  will 
eventually  overflow  the  land.  It  may  be  supposed  the  tenor  of 
past  history  argues  for  the  future  higher  elevation  of  the  land 
surfaces  and  deeper  depression  of  the  ocean's  bottom.  But  we 
shall  see  that  this  anticipation  is  rendered  nugatory  by  another 
one. 

If  the  earth  has  been  cooling  from  a  highly  heated  condition, 
and  still  radiates  more  heat  than  it  receives  from  the  sun,  we 
have  ground  for  affirming,  first,  that  the  time  will  come,  if  it  has 
not  arrived,  when  the  thermal  energy  contained  within  will  be 
too  feeble  for  the  continued  uplifting  of  continents  and  deepen- 
ing of  ocean  basins;  and  thus  the  results  of  denudation  will 
accumulate  indefinitely. 

If  the  earth  still  retains  residual  heat,  from  the  era  of  primi- 
tive incandescence,  then  the  cooled  crust  will  continue  to  thicken, 
as  this  heat  escapes  into  space.  With  the  deepening  of  the  cooled 
zone,  additional  water  will  be  received  in  the  pores  of  the  earth. 
Calculations  based  on  the  absorbent  capacity  of  average  rocks 
show  that  the  entire  ocean  is  destined  to  be  absorbed  by  the  crust 


490  GEOLOGICAL   STUDIES. 

of  the  earth.  It  appears,  even,  that  the  capacity  of  the  pores 
will  be  sufficient  to  receive  the  atmosphere  also.  The  earth  will 
hang  in  space  without  water  or  air.  When  the  atmospheric  en- 
velope no  longer  exists,  the  sun's  heat  will  no  longer  be  blanketed 
in.  The  solar  rays  will  be  returned  as  rapidly  as  received,  and 
the  terrestrial  surface  will  sink  toward  the  temperature  of  exter- 
nal space. 

The  action  of  the  moon  on  the  lunar  tidal  protuberance  is 
destroying  the  earth's  rotary  motion  (page  299).  A  period  may, 
therefore,  be  anticipated  when  the  earth  will  turn  constantly  the 
same  side  toward  the  moon.  If  then  the  moon  continues  to  re- 
volve in  the  same  period,  each  side  of  the  earth  will  be  exposed 
constantly  two  weeks  to  the  scorching  rays  of  the  sun,  to  be 
turned  during  the  next  two  weeks  into  the  shadow,  and  exposed 
to  the  intense  cold  of  planetary  space. 

But  the  moon  will  gradually  recede  from  the  earth,  and  will 
suffer  a  diminution  of  its  tide-producing  power,  and  of  its  power 
to  impress  the  earth's  rotation.  If  then  the  earth's  distance 
from  the  sun  remains  about  the  same,  the  sun's  action  on  the  solar 
tide  will  tend  to  reduce  the  rotary  motion  of  the  earth  to  synchro- 
nism with  its  annual  motion.  One  side  of  the  earth  will  then  be 
turned  continually  toward  the  sun,  and  the  opposite  side  contin- 
ually away  from  it.  This  train  of  contingencies  might  even  be 
traced  further;  but  that  is  here  unnecessary. 

The  tendency  of  the  diffusion  of  heat  to  a  state  of  equilibrium 
threatens  not  alone  the  final  refrigeration  of  the  earth.  The  sun 
is  inevitably  approaching  a  state  of  final  extinction.  His  light  and 
heat  will  eventually  become  sensibly  less;  and  in  the  distant  asons 
of  eternity  the  sun  will  become  a  dark,  cold  world. 

Such  eventualities  might  be  traced  still  further.  But  it  is 
not  appropriate  here  to  pursue  reflections  which  verge  so  nearly 
on  the  domain  of  speculation.  The  purpose  has  been  simply  to 
illustrate  the  legitimacy  and  safety  of  reasoning  from  known 
principles  to  conclusions  which  lie  even  in  the  depths  of  the 
future  eternity;  and  to  show  that  the  future  conceals  eventuali- 
ties which  must  terminate  the  period  of  human  existence  on  the 


HISTORICAL   GEOLOGY.  491 

earth.  It  is  useful,  also,  to  be  reminded  how  small  a  speck  of 
existence  we  are,  and  how  brief  an  instant  of  duration  is  covered 
by  a  human  lifetime,  or  the  lifetime  of  a  race.  Arid  assuredly, 
in  the  presence  of  such  conceptions  as  those,  we  may  feel  a 
swelling  admiration  of  that  spiritual  capacity  in  man  which 
enables  him  to  grasp  and  comprehend  the  events  of  periods  past 
and  to  come  which  stretch  out  into  the  realm  of  eternity.  It  is  a 
belief  ingrained  in  the  texture  of  the  human  soul,  that  a  being 
whose  thought  thus  rises  superior  to  all  time  and  space  and 
change  is  destined,  however  brief  his  corporeal  sojourn,  to  out- 
live in  consciousness  all  the  mutations  compassed  by  the  horizon 
of  his  thought. 


INDEX. 


NOTE. — An  asterisk  (*)  affixed  to  the  number  of  a  page  indicates  an  illus- 
tration on  that  page,  of  the  species  or  subject  mentioned.  A  dagger  (f) 
indicates  a  definition  or  explanation  of  a  term;  but  it  is  used  only  where 
more  than  one  reference  exists. 


Abyss  of  Atlantic,  86. 

Acadian,  coal  field,  406;  formation, 

362,  369,  378. 
Acanthodes,  333. 
Accessory  minerals,  51. 
Accidents  of  stratification,  256,  257. 
Acervularia,    214;    Davidsoni,    214, 

216*. 
Acidic,  feldspars,  27*,  53,  54;  rocks, 

71. 

Acids,  how  formed,  19,  20. 
Aclinal  mountains,  168. 
Acrogens,  418. 
Actinolite,  31. 
Adams,  Fort,  85. 
Adductor  muscle,  231. 
Adirondack  Mountains,  160. 
,  270. 


,  map,  371*,  383*,  399*,  423*, 
439*,  440*,  477*;  sections,  480*. 

..Etna,  eruption  of,  in  1865,  140  seq.; 
map  of,  141*. 

Affinity,  chemical,  19;  elective,  20; 
weakened  by  heat,  21. 

Agassiz  Lake,  452,  485. 

Agate,  24. 

Age,  evidences  of,  265. 

Age  in  classification,  270. 

Air  breathers,  420. 

Alabama,  iron,  184;  rocks,  384;  sec- 
tion through,  430*,  fossils,  402, 
434;  coal,  416;  cretaceous,  429. 

Alabaster,  65,  66. 

Alaska,  diamonds,  24f;  glacier,  281. 

Albany  capitol  granite,  53. 

Alberfite,  68f,  69,  195,  198. 

Albert  mine,  398. 

Albite,  27. 


Allegheny  Mountains,  93.  See  "Ap- 
palachian." 

Allodon,  347. 

Allotheria,  347. 

Alluvial,  81f,  83. 

Alps,  structure  of,  171,  172*. 

Aluminous  rocks,   60;   matter,   197. 

Alveolites,  222,  223,  225;  Goldfussi, 
222*,  223*. 

Alveolus  of  belemnite,  433. 

Amazons  River,  280. 

Amber,  68. 

Amblypoda,  351. 

Amenia  iron,  37. 

Amethyst,  24. 

Ammonites,  327;  serpentinus,  330*. 

Ammonoidea,  328,  329,  428,  433. 

Amreba,  319*. 

Amphibians,  position  of,  104;  com- 
prehensive, 316;  separated  by  gaps, 
317. 

Amphibole,  31. 

Amphibolic  rocks,  52,  249. 

Amphibolite,  52. 

Amphigenite,  72. 

Amphilestes,  346. 

Amphitheriurn,  346*. 

Am  plexus,  204,  207;  Shumardi,  204*; 
Yandelli,  207*. 

Amygdaloid,  156. 

Amygdule,  264. 

Analysis  of  minerals,  17. 

Anchippodus,  349. 

Anchitherium,  356. 

Andalusian  earthquakes,  456. 

Andalusite,  52. 

Andesite,  72. 

Animals  classified,  306-314. 


493 


494 


INDEX. 


Ann  Arbor,  Drift  at,  5*. 

Annularia,  418*. 

Anodonta  angustata,  227*. 

Anoinodontia,  341. 

Anorthite,  28. 

Anterior  of  shell,  228. 

Anthozoa,  322. 

Anthracite,  67,  69,  407,  432. 

Anticipation  of  discovery,  318. 

Anticlinal,    161f;    mountains,    167; 

axis,  261. 
Antiseptum,  210f. 
Antitide,  297. 
Antwerp,  N.  Y.,  70. 
Apatite,  367. 
Apatosaurus  Ajax,  339. 
Apertural  gap,  211. 
Aphanite,  52,  56,  57. 
Appalachian  coal  field,  406,  423. 
Appalachians,  faults  and  erosion,  93, 

94,    473*;    chain,    160,    467,    469; 

section   across,   170*;    folds,  292, 

370,  471;  strata  in,  375,  390,  398; 

glaciated,  482. 
Aral  Sea.  189. 
Archaean,  361. 
Archaeopteryx  macroura,  342*,  343, 

345. 

Arched  Rock,  393. 
Ardiche,   volcanoes   of,   149*;   table 

mountains  of,  153*. 
Area  of  Brachiopod,  231. 
Argentite,  184. 
Argillaceous,  46,  60,  249. 
Argillite,  61. 

Arizona,  184;  lava  sheets,  154. 
Arkansas,  66 ;  stones,  49 ;  coal  meas- 
ures, 406. 
Armature,  232f  seq. ;  wanting  in  some 

genera,  238. 
Arm    of    Crinoid,    324*f,    325*;    of 

Cephalopod,  326. 
Arm  supports,  232. 
Arnot  coal  mines,  414*. 
Artiodactyla,  351. 
Asbestos,  31. 
Ashes,  volcanic,  72,  286. 
Asphalt,  68,  69,  194,  198. 
Association  of  minerals,  55. 
Assortment  of  sediments,  283,  268, 

398. 

Asterophyllites,  418*. 
Athyris  spiriferoides,  235*. 


Atlantosaurus  immanis,  338. 
Atmosphere,  agency  of,  284. 
Atoms,  size  of.  18; 'kinds  of,  19. 
Attitudes  of  strata,  260. 
Atrypa,  234,  241;  reticularis,  234*, 

235*. 

Augite,  32*,  290. 
Augitic  eruptive  rocks,  72. 
Austria,  193. 
Autun,  194. 
Axis,  structural,  260. 
Azoic  System,  362. 
Azygos  plates,  325. 


Bad  Lands,  443*. 

Baker  oil  region,  199,  200. 

Bald  Eagle  Mountain,  93*. 

Ball,  R.  S.,  on  primitive  tides,  300. 

Baptanodon  discus,  336*. 

Bai-aboo  quartzite,  363. 

Bar,  279;  of  Mississippi,  85,  279. 

Barrande,  J.,  on  colonies,  304;  pri- 
mordial, 370. 

Basal  plates,  325. 

Basalt,  72. 

Basaltic,  columns,  155*;  lava,  149; 
structure,  264. 

Basic,  feldspars,  53f,  54;  rocks,  71. 

Basin,  Province,  435,  436,  438,  472; 
lakes,  452 ;  ranges,  435. 

Basins  of  hot  springs,  133*. 

Basse tt,  D.  A.,  on  Crinoids,  402. 

Bathmodon,  348,  349. 

Bathyopsis,  351,  353. 

Beak  of  shell,  226. 

Bedded  vein,  181. 

Bed  Rock,  2. 

Belemnite,  428,  433. 

Beluga  Vermontana,  457. 

Bennett,  I,  485. 

Benzole,  69,  194. 

Bex,  189. 

Big  Horn  Mountains,  374,  431. 

Biotite,  30 :  associates  of,  55. 

Birds,  position  of,  104,  316 ;  compre- 
hensive, 317;  toothed,  343*,  344*. 

Bitterns,  188. 

Bituminous,  sandstone,  46;  sub- 
stances, 194;  rocks,  250. 

Bivalves,  82,  226. 

Bivalvular  symmetry,  228. 

Black  Hills/374. 


INDEX. 


495 


Black  Shale,  391. 

Blake,  W.  P.,  on  sand  action,  284. 

Blossburg  coal  mines,  415*. 

Blowpipe  analysis,  17. 

Bog,  iron,  llf,  37,  70;  manganese, 
12. 

Bonneville  Lake,  452,  457. 

Bore  of  Hoogley,  288. 

Boissons  glacier,  281*. 

Bothriolepis,  333  ;  Canadensis,  334*. 

Botryoidal  limonite,  37. 

Bove,  val  del,  143. 

Bowlders,  defined,  4*;  particularly 
described,  12  seq.\  on  coasts,  15; 
of  copper,  15;  derived  from  north, 
15  ;  not  homogeneous,  1  G  ;  result- 
ing from  weathering,  95*,  96*. 

Brachiopods,  how  to  study,  226; 
structures  of,  classified,  240;  table 
for  determination  of,  240. 

Bramatherium,  354. 

Brasenice  purpurea,  475. 

Brazilian  pebbles,  24. 

Breadth  of  outcrop,  260. 

Breaks  in  succession  of  life,  317;  of 
rocks,  377. 

Breasts,  in  mining,  414f. 

Breckenridge  coal,  194,  409. 

Bridge  of  travertin,  132. 

British  formations,  275. 

Brittleness,  251. 

Brixham  cavern,  460. 

Brontotherium  ingens,  353*. 

Brown  coal,  68  ;  spar,  36. 

Bruin  Lake,  85. 

Buena  venture  conglomerate,  406. 

Buffalo,  201. 

Buhl,  194. 

Building  stones,  48. 

Bunsen  on  geysers,  134. 

Burlington  Stage,  395,  397,  400. 

Butte  county,  151. 


Caenozoic  Great  System,  441  ; 

470. 

Caesars,  palace  of,  64. 
Calamarians,  418*. 
Calaveras  county,  151. 
Calcareous  rocks,  61,  249. 
Calciferous  Stage,  369,  375. 
Calcite,  34*f,  35,  61,  303. 
California,  lava  beds,  154;   geology. 

383,  398,  406,  467;   province,  485. 


Calumet  and  Hecla,  367. 
Calyrnene  Blumenbachii,  323. 
Calyx,  of  coral,  203f;  crinoid,  324*f, 

Cambrian,  life,  315,  317,  323,    379; 

System,  369,  377*. 
Camel,  357. 

Carneo  mountains,  161f. 
Campbell,   J.  L.,  on  Appalachians, 

169,  170*. 

Canadian  formations,  275,  370;  mar- 
bles, 365;  Group,  269,  374,  375. 
Canals  of  Eozoon,  320. 
Canary  Islands,  145. 
Canons  of  Colorado,  89,  91,  165*. 
Cape  Cod,  448. 
Carbon,  source  of,  422. 
Carbonaceous  rocks,  67,  249. 
Carboniferous,    limestone,   197,    395, 

396,  397;  life,  315. 
Cardinal  process,  231. 
Cannae  or  carinations,  213. 
Carinatae,  316. 
Carinthia,  70. 
Carlisle  cave,  457. 
Carrara  marble,  62. 
Carson  Lake,  453. 
Cascade  Range,  441,  478;  volcanoes 

of,  147;  coal  in,  432. 
Caspian  Sea,  189. 
Cast  of  fossil,  66f,  304. 
Castle  Rock,  377*. 
Castle  Rock  Range,  167. 
Castoroides  Ohioensis,  459*. 
Cast,  up  and  down,  in  mining,  414. 
Cataclysmic  theory,  456. 
Catania,  143. 
Catskill,    Mts.,    161*;     Group,   191, 

389,  390,  398. 
Cauda-galli  Grit,  390. 
Caverns,   277,  454;    quadrupeds  in, 

457,  460. 
Cavicornia,  354. 
Cell  of  coral,  203f,  219. 
Cement  in  rocks,  47. 
Central  gap,  21  If. 
Centre  county,  Pa.,  93. 
Centronella,    233,    241;    Julia,    233, 

238*. 

Cephalaspis  Lyelli,  333*. 
Cephalic  shield,  323. 
Ceratites,  327,  328,  329. 
Ceratodus,  333. 


496 


INDEX. 


Cestracionts,  332*,  402,  434. 

Chalcedony,  24. 

Chalcopyrite,  184. 

Chalk,  64 ;  effervescence,  20 ;  precip- 
itated, 21 ;  red,  37;  French,  59. 

Challenger,  326. 

Chalybeate  water,  12. 

Chambered  shells,  326f,  389. 

Chamberlin,  T.  C.,  365,  374;  on 
Drift,  447,  451,  448. 

Chambers,  326. 

Champlain  formation,  441, 452 ;  Lake, 
457;  epoch,  483. 

Charmoz,  Mt.,  166*. 

Chazy  Stage,  369,  375. 

Cheeks  of  trilobite,  324. 

Cheirolepis,  333. 

Chelysoma  Maclovianum,  334*. 

Chemical  affinity,  19f ;  study  of 
rocks,  253. 

Chemistry,  rudimentary  principles, 
18  seq. 

Chemung  Group,  192,  194,  389,  391. 

Chert,  25. 

Chester,  salt  at,  188. 

Chester  Stage,  395. 

Chicago,  198,  382,  385. 

Chico  Group,  431,  432. 

Chief  septum,  210. 

Chilhowee  Sandstones,  374. 

Chimaerae,  431. 

Chlorides,  19. 

Chlorite,  31,  52. 

Chonetes,  402. 

Chromic  iron,  431. 

Cincinnati,  81,  382,  445,  446;  Stage, 
369,  470;  sub-Group,  197,  376, 
378. 

Cincinnati  swell,  378,  379*. 

Circumdenudation,  263. 

Cladopora,  223,  225;  Rcemeri,  223, 
224*;  laqueata,  224*. 

Classification,  of  formations,  269, 
274,  275;  of  fossils,  303,  305-314. 

Claypole,  E.  W.,  mountain  folds,  171, 
292. 

Cleavage,  35f. 

Clermont,  France,  travertin,  132*. 

Cleveland,  gas  at,  201. 

Cliff  Limestone,  391,  392*. 

Climates,  geological,  106,  295;  ex- 
tra-terrestrial causes,  297;  relation 
of,  to  Drift,  446. 


Clinodactyla,  351. 

Clinton  Stage,  381. 

Clisiophyllum,  204;  Oneidaense,  204. 

Clouded  marble,  62. 

Clouds,  first  formed,  464. 

Clymenia,  327;  family,  330. 

Coal,  67;  brown,  68;  origin  of,  421. 

Coal  conglomerate,  oil  in,  196. 

Coal  Measures,  described,  402  seq., 
471 ;  standard  section  of,  403 ;  iron 
in,  183;  brine  in,  192;  disturb- 
ances in,  410,  411. 

Coal  Period,  470,  471;  Fields,  406. 

Coal  plants,  416;  tar,  67,  194. 

Coal,  Cretaceous,  422,  433. 

Coast  Ranges,  435,  443,  474. 

Cobble  stones,  4. 

Coccosteus  decipiens,  333*. 

Cceluria,  343. 

Ccenostroma,  321 ;  monticuliferum, 
322. 

Coke,  67. 

Cold  short,  70. 

Colloid,  251. 

Colonies  of  fossils,  304. 

Colorado,  94,  98,  397,  406,  426,  428, 
478;  coal  in,  432. 

Colorado  Range,  163,  434,  468;  pla- 
teau, 165. 

Colorado  River,  434,  441,  476;  ero- 
sion, 89,  91*,  455. 

Columbia  River,  148,  154. 

Column,  geological,  107*,  274. 

Columnar  basalt,  155*,  156*. 

Comb  in  veins,  180. 

Commissure,  237. 

Como,  427. 

Compactness,  252f. 

Composition,  of  minerals,  Table  ofy 
40;  rocks,  Table  of,  75. 

Comprehensive  types,  316f,  318. 

Comstock  Lode,  184,  185. 

Concentric  structure,  47. 

Concretionary  structure,  258, 

Concretions  of  iron,  47;  sandstone, 
48*. 

Condylarthra,  350. 

Cone  in  cone,  287*f. 

Cones,  volcanic,  146,  147*;  hollowed 
out,  147*;  near  Mono  Lake,  148; 
in  central  France,  149. 

Coney  Island,  99. 

Conformability,  lOOf,  263. 


INDEX. 


497 


Conglomerate,    25;     quartzose,    45; 

Carboniferous,  196,  405,  406;  Ke- 

weenian,    366;     Cretaceous,    439, 

440. 

Conifers,  475. 
Connecticut,    iron    in,    184;     rocks, 

424,  425,  472. 

Connecticut  River,  81,  455. 
Conspectus  of  extinct  life,  359*. 
Constitutive  ingredients,  38f. 
Contact  vein,  181. 
Continent,    growth    of,    371*,    382, 

383*,  399*,  423*,  441,  475;  physi- 
ognomy of  interior,  434. 
Contorted  folds,  262f. 
Contraction  of  earth,  174,  175;  and 

earthquakes,  292. 
Cook,  G.  H.,  on  subsidence,  487. 
Cooling,   earth,  158,  174;  effects  of, 

291,  489;  sun,  296. 
Cope,  E.  D.,  on  reptiles,  337;  mam- 
mals,   348;    Port   Kennedy  cave, 

457. 

Copper-bearing  formation,  362. 
Copper,  bowlders,  15;  pyrites,  184. 
Copper,  occurrence  of,  184,  367,  431. 
Corals,  Cup,  203,  387;  Silurian,  387; 

Devonian,  394. 
Cordaites,  418. 
Cordilleran  Land,  364,  372,  378,  382, 

383,  384,  467,  468. 
Cordilleran    region,    400,    436,  443, 

476 ;  geological  history  of,  437. 
Cordilleras,  436. 
Corniferous  Limestone,  197,  390,  391, 

392,  451. 
Corrasion,  264. 
Coryphodon  hamatus,  348*. 
Cost®,  204f. 

Cotta,  von,  on  veins,  181. 
Cottonwood  River,  165. 
Council  Bluff,  445. 
Country  rock,  69,  180. 
Crater  of  Vesuvius,  138. 
Crater  of  Vesuvius  in  1756,  146*;  of 

Tjeendoeng,  146*. 
Crawfordsville  crinoids,  401. 
Cretaceous,  System,   424,   429,  439, 

440,  441,  474;  ^Eon,  close  of,  474. 
Crinoids,   324*,   380,   387,    476;    at 

Crawfordsville,  402. 
Croll,  J.,  on  glaciation,  485. 
Crumpling,  263. 


Crust,  11  If,  246;  fire-formed,  287; 
incipient,  464. 

Crustaceans,  402. 

Cryptocrystalline,  54,  251. 

Crystalline  form  of  quartz,  24* ;  feld- 
spar, 26*,  27*;  calcite,  35*;  mag- 
netite, 38*. 

Crystalline  rocks,  45,  70,  250f. 

Crystallization,  22,  56. 

Ctenacanthus,  333. 

Ctenacodon  serratus,  347*. 

Cuba,  198. 

Cumberland,  Table  Land,  161,  407; 
River,  196. 

Cup  corals,  202  seq. ;  how  studied, 
203;  cup  of,  203;  table  of,  217; 
Lower  Carboniferous,  401. 

Cup  of  crinoid,  324. 

Currents,  oceanic,  279,  293. 

Cyathophyllum,  204*,  208*;  corni- 
cula,  204*. 

Cycads,  420,  475. 

Cycle  of  sedimentation,  268f,  284, 
409. 

Cynodraco,  341*. 

Cyrtina,  231,  241;  Hamiltonensis, 
231*. 

Cyrtoceras,  329;  Eugenium,  330*. 

Cyrtoceratidae,  328. 

Cystiphyllum,  213,  214,  217;  Amer- 
icanura,  214*,  215*. 

Dakota,  185,  430,  445,  448. 

Dalles  of  Wisconsin  River,  89*,  377. 

Danan,  145. 

Dartmoor,  194. 

Darwin,  C.,  on  sediments,  283. 

Daubree  on  metamorphism,  290. 

Davenport,  445. 

Davis  cut  off,  85. 

Dawn  animal,  318. 

Dawson,  G.  M.,  great  bowlders,  13. 

Dawson,  Sir  W.,  coal  plants,  418*, 

419*;  Laramie  plants,  475. 
Dead  rock,  416. 
Deformative  tide,  298. 
Delta,  of  rivers,  279;  of  Mississippi, 

84 

Deltidium,  231*. 
Denudation,  96f,  101,  263;  rate  of, 

278 ;  finality  of,  489. 
Des  Chutes  River,  154. 
Des  Moines,  445. 


498 


INDEX. 


Determination  of  minerals,  42-4 ;  of 

rocks,  Table  for,  76-80. 
Detritus  in  ocean,  293. 
Devonian,    Life,  315,  322;    System, 

389. 

Diabase,  54;  eruptive,  71. 
Diallage,  32,  3GO. 
Diamond,  69. 

Diamond  Peak  Quartzite,  397. 
Diaphragms,  207. 
Diastema,  353. 
Diclonius,  475. 
Dicynodon  lacertipes,  341*. 
Dicynodontia,  341*. 
Dikes,  155*,  156*,  427;   as  bearing 

on  age,  266. 

Dimophodon  macronyx,  342*. 
Dinichthys  Herzeri,  331*,  332. 
Dinoceras,  351 ;  mirabile,  351*,  352*. 
Dinocerata,  351. 
Dinosauria,  338. 
Dinotherium,  353*. 
Diorite,  53,  54 ;  eruptive,  71 ;  quartz, 

72, 
Dip,   100,  260;    rule  of,  114*,    117, 

120,  121. 
Diphyphyllum,  215,  218;   Archiaci, 

216*. 

Diplacanthus,  333. 
Diplocvnodon  victor,  347*. 
Dirt  beds,  448. 

Dislocation,  163.     See  "Faults." 
Dissepiments,  208. 
Dissipation  of  heat,  296,  490. 
Dissociation,  21. 

Distribution  wide  in  early  times,  106. 
Divaricator  muscle,  231*. 
Docodon,  347. 
Dog-tooth  spar,  35*. 
Dolerite,  72,  184. 
Dolomite,  36,  61. 
Dolomitic  limestone,  63,  249. 
Dorsal  valve,  227. 
Drainage  of  lakes,  452. 
Drift  2f,   3*,    5*;    formation,   441; 

described,  444  seq.;  northern  and 

southern,  445-6,  and  climate,  446 ; 

at    Ann    Arbor,    6;    fossils,  394; 

limestone  masses  in,  451. 
Drift  in  mining,  413. 
Drift  structures,  256. 
Dromatherium  sylvestre,  345,  346*. 
Drummond's  Island,  385. 


Dryolestes,  347. 

Dunes,  285. 

Durability,  252. 

Dust,  cosmic,  286. 

Dutton,  0.  E.,  90,  91;  on  Hawaii, 
143;  on  San  Mateo  Mountains, 
154;  lateral  pressure,  292. 

Dyas,  403. 

Dynamical  geology,  246f,  276  seq. 

Eagle,  Wis.,  moraine,  450,  451*. 
Earthquakes.    292;   and    volcanoes, 

143. 

Earthy,  250. 

Eastern  interior  Coal  Field,  406. 
East  Rock,  155. 
Ebb  and  flow  structure,  256. 
Echo  cliffs,  164*. 
Economic,  Geology,  246 ;  products  of 

Eozoic,  365. 

Edestosaurus  dispar,  338*. 
Effervescence,  17;  of  chalk,  20. 
Egyptian    marble,    62;    asphaltum, 

198. 

Elasmobranchs,  331,  332. 
Elasmosaunis  platyurus,  337*. 
Elba,  geology  of,  157*. 
El  Dorado  county,  151. 
Elements,  18,  19. 
Elephas      Americanns,     447,    458*; 

primigenius,  457,461*;  Africanus; 

458*;  Indicus,  458*. 
Elk  Mountains,  425. 
Elongation  of  Mountains,  293. 
Emery,  38. 

Emmons,  E.,  on  mammals,  345*. 
Enstatite,  366. 
Eobasileus,  351,  352*. 
Eocene,  442. 
Eohippus,  354. 
Eosaurus  Acadianus,  355. 
Eozoic,    Great    System,    361,    465; 

JEon,  465. 

Eozoon,  317,  318*  seq.,  380,  466. 
Epidote,  38,  52. 
Epihippus,  256. 
Epitheca,  204. 
Epoch,  270. 
Equidre,  355. 
Equine  types,  355. 
Equiseta,  418. 
Equivalents,     stratigraphical,     271 ; 

table  of,  273,  274. 


INDEX. 


499 


Equus,  354,  357. 

Erie  clays,  452,  486. 

Erie  Lake,  449. 

Erosion  of  mountains,  160. 

Erosions,  87  seq.,  263,  264;  rate  of, 
95;  some  effects  of,  109,  488; 
Cambrian,  376;  Silurian,  386:  De- 
vonian, 392;  Lower  Carboniferous, 
401. 

Erupted  conditions,  264. 

Erupted  materials,  origin  of,  289. 

Eruptions  of  Vesuvius,  138;  JEtna, 
140,  143;  Krakatoa,  145;  ancient, 
150  seq.;  Triassic,  427. 

Eruptive  rocks,  70;  mountains,  168. 

Eureka  district,  410. 

European  formations,  275. 

Eusthenopteron,  333. 

Eutaw  Group,  429. 

Evanston  coal,  432. 

Exogyra  costata,  433. 

Expansion  of  organic  types,  359. 

Explosions  from  volcanoes,  143. 

Extinctions  of  organic  types,  314. 

Eyes,  compound,  323. 

Faces  of  quartz,  24;  feldspar,  215. 

Fall  Brook  coal  mines,  414. 

Falls,  Trenton,  Glen's,  Minnehaha, 
High,  377;  Ohio,  394. 

False  coal  measures,  398,  406. 

Fan  structure,  171. 

Faults,  163,  164*,  165;  in  Colorado 
plateau,  175,  437;  in  Appalachi- 
ans, 407;  Illinois,  410;  resulting 
from  flexure,  261*,  295 ;  and  repe- 
tition of  strata,  266. 

Faunas,  why  changing,  103. 

Favistella,  380. 

Favosites,  219,  222;  favosus,  219*, 
220*;  Alpenensis  (Hamiltonensis) 
219*,  220,  221*;  tuberosus,  219*; 
nitella,  219*,  221*;  clausus,  219*; 
Canadensis,  222*. 

Favositidas,  224,  387. 

Favre  on  mountain  folds,  174. 

Feather- form  septa,  210. 

Feldspar  studied,  25;  angles  of,  26*; 
common,  27;  acidic  and  basic,  27; 
species  of,  27;  discrimination  of, 
28. 

Feldspathic,  eruptive  rocks,  7; 
rocks,  249. 


Felsite,  57. 

Felsitic  rocks,  56  seq. 

Fentress,  N.  C.,  70. 

Ferns  in  coal  measures,  416*;  in 
Mesozoic,  475. 

Ferns,  living  tree,  417. 

Ferriferous  Limestone,  408. 

Ferruginous,  water,  12;  sandstone, 
46;  rocks,  249. 

Findlay  gas  wells,  201. 

FingaP's  cave,  154,  264. 

Fire-clay,  60. 

Fire-formed  crust,  287;  disappear- 
ance of,  287,  288*. 

Firehole  River,  135,  136. 

Firemist,  JEon,  463. 

Fisher,  O.,  on  lateral  pressure,  292. 

Fishes,  331.  470. 

Fishes,  comprehensive,  316;  separ- 
ated by  gaps,  317. 

Fissure  in  Brachiopods,  231*. 

Flaming  Gorge  Group,  424,  427. 

Flexure,  262. 

Flint,  24;  in  chalk,  64. 

Floating  ice,  280. 

Floe-till,  447. 

Floods,  Champlain,  484,  486. 

Floors  in  cup  corals,  207. 

Florida,  443,  459. 

Fluidal  texture,  251. 

Fluviatile,  81. 

Fold  in  Brachiopods,  228. 

Folds,  in  Appalachians,  171 ;  moun- 
tain making,  172*,  173*,  262*; 
how  caused,  175*. 

Fontaine,  W.  M.,  on  Jura-Trias, 
345,  425. 

Foot  of  mollusc,  226. 

Foraminifera,  86,  322. 

Formation,  255f. 

Formational  Geology,  246,  360. 

Fort  Adams,  85. 

Fossa  or  fossette,  203. 

Fossils,  99,  102,  256f,  303;  condi- 
tions of,  303;  classification  of, 
305-314;  what  they  teach,  102; 
distinguishing  strata,  103;  indi- 
cating age,  266. 

Foster  and  Whitney,  362. 

Fovea,  203. 

Fragmental  rocks,  45,  46,  250f,  268, 


Franklinite,  69,  183. 


500 


INDEX. 


Fraas  on  mammoth,  461. 
Freestones,  48. 
Freiberg,  180. 
Fremont  gas  wells,  201. 
Friability,  252. 
Friable,  45. 

Frumento,  Monte,  141. 
Fumarole,  140. 
Fundy,  Bay  of,  280. 
Funnel  of  Cephalopod,  326. 
Fusion  beneath  crust,  288*. 


Gabbro,  53,  366.     See  "Norite." 

Galastes,  347. 

Galena,  184;  cave,  457;  Limestone, 

375. 

Game,  lithological,  55  note. 
Ganges,  278. 
Gangue,  180. 
Gangways,  414. 
Ganoids,  331f,  402,  476. 
Gaps  in  Corals,  211;  in  organic  suc- 
cession, 317. 

Gaps,  stratigraphical,  271. 
Garnet,  38. 

Gas,  inflammable,  68,  69,  201. 
Gas  rock.     See  Table,  403. 
Gasteropods,  444. 
•Gay  Head,  15,  99. 
Geanticlinal,  295. 
Gemmation,  220. 
Genesee  River,  88  ;  Shale,  194,  195, 

389,  391. 
Geognosy,  255. 

Geographical  range  of  fossils,  304. 
Geological  column,  107*. 
Geology,  If,  245f  ;  subdivisions  of, 

245,  246. 

Georgia,  381,  416,  443,  473. 
Georgian  Bay,  382. 
Georgia  oil  region,  199. 
Geosynclinal,  205,  470. 
Geotechtonic  results,  302. 
Geysers  of  National  Park,  134  seq.; 

action  of  explained,  134. 
Giant  Geyser,  135. 
Giant's  Causeway,  154,  264. 
Gilbert,  G.  K.,  on  Henry  Mountains, 

157;  sand  action,  284;  Quaternary 

lakes,  452. 

Gilsum  bowlder,  13*. 
Glabella,  323. 


Glacial  formation,  441 ;  epoch,  479 ; 

pressure,  485. 

Glaciers,  280 ;  continental,  481 ;  pres- 
sure of,  485. 
Glance,  silver,  184. 
Glasgow,  Ky.,  197. 
Glass,  how  made,  49. 
Glauconite,  431. 
Globigerina,  86. 
Gloucester  bowlders,  4*. 
Glyptodon,  459. 
Glyptolepis,  333. 
Gneiss,  50,  51;  syenitic,  52;  species 

of,  54 ;  protogine,  59 ;  chloritic,  60. 
Gold,  185,  431 ;  associates  of,  185. 
Goniatites,  327*,  402. 
Gorge  of  Niagara,  89;  Colorado,  90, 

437;  Hudson,  455*. 
Gorges,  454. 

Graham ite,  68f,  69,  195,  198. 
Grand  Canon,  437. 
Grand  Detour,  411. 
Grand  Gulf,  85. 
Grand  Haven  dunes,  285. 
Grand  Rapids,  65. 
Grand  Wash  fault,  164*. 
Granite,    50f,    51,    52;    Scotch,    53; 

Quincy,  53;  eruptive,  71,  291. 
Granular  texture,  45,  250f. 
Granulite.  51;   gneiss,  51;  eruptive, 

71. 

Graphite,  67,  69,  367,  470. 
Gravel,  4f. 

Graylock  Mountain,  165*. 
Great  Basin,  435. 
Great  Britain,  formations,  275. 
Great  Northern  Land,  363,  372f,  467, 

468,  469. 
Great  Plains,  372,  400,  429,  434,  438, 

440,  443,  468,  478,  483. 
Great  Salt  Lake,  453. 
Great  System,  278. 
Greenland,  282,  482,  485;  icebergs, 

283. 

Green  River,  162. 
Green  sand,  431, 
Greisen,  50. 
Grindstones,  49. 
Gritstones,  396. 
Group.  270. 
Growth,  lines  of,  231. 
Gryphaea  mutabilis,  433. 
Gum  beds,  198. 


INDEX. 


501 


Gymnosperms,  418. 

Gypsum,  36*,  65,  66,  192,  386,  397, 

427. 
Gyroceras  undulatum,  330*. 

Habitability  of  North  Pole,  295. 

Hadrosaurus  Foulki,  339*. 

Haematite,  36,  69,  183;  stalactitic, 
37;  micaceous,  37;  ochery,  37;  jas- 
pery,  69;  argillaceous,  70;  oolitic, 
70;  sedimentary  in  origin,  183. 

Haleakala,  145. 

Hall,  James,  on  spires,  235. 

Halleflinta,  57. 

Hamilton  Group,  194,  195,  389,  391. 

Hard  heads,  13. 

Hardness,  standards  of,  42;  of  rocks, 
251. 

Hard  water,  12. 

Hawaii,  described,  143;  map,  144*; 
profile,  144*. 

Hawkins,  B.  W.,  340. 

Heat,  dynamic  agency  of,  286;  evo- 
lution of,  292,  298;  total  dissipa- 
tion of,  296. 

Helderberg,  Mountains,  381,  386; 
Group,  386. 

Heliophyllum,  213;  Halli,  213*,  214*. 

Henry  Mountains,  157*,  168,  437. 

Herculaneum,  138. 

Hesperornis  regalis,  343*,  344*. 

Heterocercal,  332*. 

Hexacoralla,  218,  401,  See  "Tabu- 
lata." 

Hexagonal  prism,  24. 

Hinge  of  mussel,  226;  of  Brachio- 
pod,  228,  229*,  230',  236*,  237*; 
mechanism,  231*. 

Historical  Geelogy,  246. 

Hitchcock,  C.  H.,  Gilsum  bowlder, 
13*. 

Hitchcock,  E.,  on  veins,  179*. 

Hipparion,  356. 

Hippopotamus,  153. 

Hippotherium,  356. 

History  of  earth  a  cooling  history, 
159. 

Hoffman,  Mt.,  95. 

Holmes,  Mt.,  158*. 

Homacanthus,  333. 

Homewood  Sandstone,  408. 

Homologies,  208. 

Hood,  Mt.,  147. 


Hoogly,  280. 

Horizon,  geological,  271. 

Horizontal  range  of  fossils,  304. 

Hornblende,  31*;  associates,  55. 

Hornblendic  rocks,  52,  249. 

Hornblendic  eruptive  rocks,  71. 

Hornets'  Nest,  376. 

Horse,  153,  459. 

Horton  Series,  398. 

Hot  springs  on  Gardiner's  River, 
133*. 

Hualalai,  Mauna,  143. 

Hudson  River  Slate,  197;  formation, 
376;  valley,  455*,  481. 

Human  implements  in  caverns,  462. 

Humboldt,  Mountains,  160  ;  Lake, 
453. 

Huron  Group,  192,  389,  391. 

Huronian  life.  315 ;  times,  466 ;  Sys- 
tem, 362,  373,  377. 

Huron  River,  6. 

Huron  Shale  (Newberry),  322. 

Hybodonts,  332. 

Hydraulic  limestone,  65. 

Hydrocarbons,  194. 

Hydromica,  30;  compounds,  51. 

Hydrous  magnesian  rocks,  58. 

Hylonomus,  335. 

Hyperclinal  mountains,  168. 

Hypersthene,  33,  366. 

Hyposyenite,  52. 

Hyracoidea,  350,  351. 

Hyracotherium, 

Ice,  action  of,  280. 

Iceberg,  283. 

Iceland  spar,  35. 

Ichthyornis  dispar,  343*. 

Ichthyosauria,  336. 

Ichthyosaurus  communis,  336*. 

Idaho,  184,  185,  397. 

Ideal  section  of  earth's  crust,  115. 

Idiostroma,  321. « 

Iguanodon,  340  ;  Bernissarten  s  i  s, 
339*. 

Illinois,  lead,  184;  rocks,  385,  386, 
391,  396,  398,  422,  445;  coal,  409, 
410,  412*;  fossils,  379,  402;  faults, 
410,  411;  dirt  beds,  448,  483. 

Impression  of  a  fossil,  305. 

Improvement  in  organic  types,  105. 

Inclinations  of  strata,  how  caused, 
101. 


502 


INDEX. 


Indiana,  fossils,  379,  401 ;  rocks,  384, 

385,  390,  403;  petroleum,  392;  coal, 

409 ;  Drift,  449. 
Inductive  method,  1. 
Injected  matter,  291. 
"In  place"  defined,  99. 
Interglacial  epoch,  483. 
Internal  heat,  292. 
Interradial  plates,  325. 
Intersections  of  veins  and  age,  267. 
Intrusive  condition,  265. 
Invertebrates,    marine,    position  of, 

103 ;  reign  of,  469. 
Iowa,  lead  in,  184;  formations,  374, 

391  ;     Carboniferous     Limestone, 

397*. 
Iron,    bog    ore,   11;    haematite,    36; 

limonite,   37;    magnetite,   37;    in 

Eozoic,  365. 
Iron  ore  rock,  69;    sedimentary  in 

origin,  183. 
Iron  regions.  183,  384. 
Ironstone,  47,  183. 
Ischia,  earthquake,  456. 
Isinglass,  30. 
Isogeothermal  planes,  288. 

Jasper,  25. 

Joggins,  coal  at,  417. 

John  Day  River,  443. 

Jointed  structure,  258*,  259. 

Jurassic,  Age,  close  of,  473;  Mam- 
mals, 316;  System,  424,  425,  427, 
438,  440. 

Jura-Trias,  424. 

Kaibab  plateau,  164* ;  structure,  437. 

Kames,  447,  450. 

Kanab  plateau  and  canon,  164*. 

Kanawha  salines,  409. 

Kansas,  430,  438,  473. 

Kaolin,  28,  60. 

Kaolinic  rocks,  249. 

Karg  gas  well,  201. 

Kea,  Mauna,  143. 

Kearsarge,  Mt,  166*,  365,  368*. 

Kentucky,   192,   194,   196,  370,  394, 

396,  403,  407,  409,  416. 
Keokuk  Stage,  395,  402. 
Kerosene,  194. 
Keweenaw  Point,  374;  bowlders,  15; 

lava  outflows  near,  156. 


Keweenian  System,  362,  363,  366,  367, 

374,  466. 

Key  West,  186,  442. 
Kidney  iron,  47,  70,  392. 
King,  'C.,  on  mountain  folds,   171; 

on  loss,  285 ;  interior  geology,  400 ; 

Quaternary  lakes,  452. 
Kirkdale,  cavern,  460. 
Knobs,  396,  401. 
Koipato  Group,  424,  425. 
Krakatoa,  eruption  of,  145,  456. 

Labradorite,  27,  366. 

Laccolite,  157*,  158*,  168,  437. 

Lackawanna  basin,  407. 

Lacustrine  deposits,  445,  452f. 

LaBlaps  aquilunguis,  343. 

Lagging  tide,  299. 

Lahontan  Lake,  452,  457. 

Lakes,  Quaternary,  452. 

Lamellibranchs,  226*;  how  differ 
from  Brachiopods,  226;  Jurassic, 
428;  Cretaceous,  433,  476;  Terti- 
ary, 444. 

Lamina,  4f,  99,  252*f. 

Lamination,  oblique,  256. 

Land,  growth  of,  106. 

Land's  End,  58. 

Laosaurus  altus,  339. 

Laramie,  Hills,  163;  Group,  431, 
432;  coal,  433;  Range,  434;  plants, 
475. 

Lassen's  Peak,  150. 

Lateral  gemmation,  221 ;  pressure, 
171. 

Lateral  pressure,  171 ;  illustrated, 
172* ;  effects  of,  291,  294. 

Lateral  septa,  210. 

Laurentian,  Mountains,  160;  life, 
315,  317,  318;  System,  362,  367, 
373;  times,  465,  466;  land.  See 
"Great  Northern." 

Lava,  Vesuvian,  71,  72,  138;  &t- 
nean,  141*;  Hawaiian,  144*;  an- 
cient, 150,  154;  tables  of,  151*, 
152*,  153*;  sheets  of,  154,  485; 
scoriaceous,  156*;  laccolitic,  157*; 
origin  of,  289,  485. 

Layer,  255f. 

Lead,  184. 

Leadville,  184. 

Leconte,  J.,  on  western  lavas,  154. 

Leda  clays,  457. 


INDEX. 


503 


Lehigh  basin,  407. 

Lenticular  vein,  181. 

Lepidodendrids,  416. 

Lepidodendron,  419*,  420. 

Lepidoganoids,  331. 

Lepidolite,  30. 

Lepidosteus,  334;  embryo,  335*;  Hu- 

ronensis,  334*;  oculatus,  334*. 
Lesley,  J.  P.,  94;  on  Coal  Measures, 

405,  406. 
Lesquereux,  I.,  on  Cretaceous  plants, 

475. 

Lestosaurus  micremus,  338*. 
Lewis,  H.  0.,  on  terminal  moraine, 

448. 

Life,  progress  of,  94,  303,  469,  475. 
Lignilites,  257. 
Lignite,  68. 
Lima  gas  wells,  201. 
Limaria,  223,  225 ;  crassa,  223*. 
Limestone,  62 ;  for  building,  65 ;  hy- 
draulic, 65. 
Limonite,  37,  70,  184. 
Lingula,  380. 
Links     missing,    317 ;     connecting, 

345*. 

Lipari  Islands,  140. 
Lithological  Geology,  246,  248,  seq. 
Lithostrotion,   215,   216*,  217,  401; 

Canadense,  216*. 
Little  Traverse  Bay,  394. 
Liverpool,  salt  near,  188. 
Loa,  Mauna,  143. 
Lobes  of  septum,  330*. 
Lode,  180. 
Lodestone,  28. 
Logan,  Sir  W.  E.,  362,  365. 
Long  Branch,  98. 
Long  Island,  442,  481. 
Longitudinality    in    folds,  wanting, 

174;  present,  175. 
Loop  of  Brachiopods,  237*,  238* 
Los  Angeles,  198,  200. 
Loss,    of   China,    285 ;    of  America, 

285,  445. 
Louisiana,  193. 
Loup  River,  Beds,  478,  479. 
Lower  Carboniferous  System,  395. 
Lower  Freeport  Coal,  408. 
Lower  Helderberg  Group,  381. 
Lower  Kittanning  Coal,  408. 
Lower  Magnesian  Limestone,    374, 

375. 


Lower  Mercer  Limestone,  408. 
Loxolophodon,  352. 
Lunar  tides.     See  "Tides." 
Lustre  of  minerals,  17;  quartz,  23; 

feldspar,  25. 
Lycosaurus,  341*. 
Lynn,  58. 


Macfarlane,  J.,  415. 

Machaeracanthus,  332. 

Mackinac,  L,  393,  451. 

Madeline  Plains,  453. 

Magnesian,  rocks,  58 ;  limestones,  62, 
374. 

Magnetite,  37,  183. 

Magnetic  corpuscles,  286*. 

Magnetic  study  of  rocks,  254. 

Mahonoy  Basin,  407. 

Maine,  382,  386. 

Mallet,  R.,  on  internal  heat,  292. 

Mammals,  position  of,  105,  316 ;  un- 
der table  mountains,  153 ;  separated 
by  gaps,  317;  descriptions  of,  345 
seq. ;  Mesozoic,  345,  476 ;  Tertiary, 
348  seq. 

Mammoth,  457,  458,  460,  461*. 

Mammoth,  Hot  Springs,  133* ;  Cave, 
277*,  401 ;  Coal  Bed,  409. 

Man,  position  of,  105,  316 ;  advent, 
462,  487;  place  in  nature,  491. 

Mandibles  of  Cephalopods,  326. 

Manganese  bog  ore,  12. 

Manitoulin,  I.,  197,  376,  384. 

Map,  nature  of,  113,  114,  372;  ex- 
plained, 116  seq.;  of  United  States, 
118-119*,  360;  interpretation  of, 
117  seq.;  to  be  read  beneath  the 
surface,  120;  exercises  on,  120- 
122;  of  North  America,  801. 

Marble,  34,  62,  63,  367,  368. 

Marble  Canon,  164. 

Marblehead,  58. 

Marcellus  Shale,  195;  Stage,  390. 

Margarodite,  30. 

Mariposa,  428. 

Marl,  llf,  64. 

Marsh,  0.  C.,  on  reptiles,  335,  336, 
428;  toothed  birds,  343;  Allothe- 
ria,  347;  Puerco,  443;  Christmas 
Lake,  453. 

Marshall,  sandstone,  191f,  192,  390; 
Group,  395,  396,  400. 


504 


INDEX. 


Marsupials,  evolving,  347;  Tertiary, 
348. 

Martha's  Vineyard,  15,  442,  444. 

Massachusetts,  386. 

Massive  structure,  16,  252. 

Mastodon,  457,  458*;  under  table 
mountains,  153. 

Mather,  on  Catskill  Mts.,  161*. 

Maui,  island,  145. 

Medicine  Bow  Range,  434,  468. 

Medina  Stage,  381,  384. 

Megalonyx,  459. 

Megalosaurus,  343. 

Megaphytum,  417*. 

Megatherium,  459,  460*. 

Melaphyr,  366. 

Memphis,  445. 

Meniscoessus  conquistus,  348. 

Menophyllum,  212*. 

Merapi,  volcano,  147*. 

Mer  de  Glace,  terminal  moraine,  282. 

Meriden  Mountains,  155. 

Meridional,  predispositions,  175 ; 
trends,  301. 

Meridionality  in  folds,  293;  when 
wanting,  173. 

Merychius,  356. 

Mesas,  168. 

Mesohippus,  356. 

Mesonyx  ossifragus,  350*. 

Mesozoic  life,  316,  475;  reptiles,  335; 
mammals,  345,  348;  Great  System, 
424;  ^Eon,  478. 

Metamorphism,  99,  121,  259f;  re- 
gional, 265;  explanation  of,  290, 
291. 

Metasomatic  change,  265f,  291. 

Mexico,  Gulf  of,  85 ;  tin  in,  185. 

Mica,  29 ;  schist,  50. 

Micaceous  rocks,  50  seg.,249. 

Michigan,  iron  in,  183,  392 ;  copper, 
184;  silver,  184;  salt,  190,  191*, 
385,  386,  397,  400;  mineral  wells, 
192;  formations,  274,  367,  370,  385, 
391.  393,  396,  469;  fossils,  394;  in- 
land salt  sea,  400;  coal  field,  406; 
Drift,  449,  451. 

Michigan  Salt  Group,  191,  192,  397. 

Microcline,  28. 

Microcrystalline,  54,  56,  251. 

Microfelsitic,  251. 

Microlestes  antiquus,  345,  346. 

Microscopic  study  of  rocks,  253. 


Migrations  of  animals,  304. 

Millstone  Grit,  405. 

Mineral,  16,  247. 

Minerals,  how  differing,  17;  chemi- 
cal compounds,  22;  some  elemen- 
tary, 22;  crystalline  forms,  22; 
reviewed,  39  seq. ;  composition  of, 
40-41;  determination  of,  42-44. 

Mineral,  water  at  Clermont,  132; 
wells  in  Michigan,  192, 

Mining  for  coal,  413. 

Minnesota,  195,  376. 

Miocene,  441. 

Miohippus,  356. 

Missing  links,  317. 

Missionary  Ridge,  161. 

Mississippi  valley,  83;  river,  83,  84*; 
erosions,  89,  90*;  sediment,  277, 
278. 

Missouri,  69,  98;  lead  in,  184;  rocks, 
396. 

Modena  oil  region,  199. 

Molten  state  of  earth,  287. 

Monoclinal  mountains  161,  165,  167. 

Mono  Lake,  volcanic  cones  near, 
148*. 

Montana,  185,  397,  406. 

Mont  Blanc,  281*,  286. 

Montreal  River,  366. 

Monument  Park,  93,  94*. 

Moon  in  terrestrial  history,  298,  299. 

Moon's  distance  increasing,  300. 

Moraines,  281,  282,  447;  terminal, 
448,  449*,  450. 

Mormon  temple  syenite,  53. 

Morosaurus  grandis,  339. 

Morris  Run  coal  mines,  414. 

Mortar,  how  made,  49. 

Mosasaurs,  434. 

Mosasaurus  princeps,  338. 

Moulds,  66;  of  fossils,  303. 

Mountain,  making,  293;  Limestone, 
396;  phenomena,  160,  293;  slides, 
92. 

Mountains,  Laurentian,  etc.,  160; 
two  classes,  160;  of  relief,  161; 
synclinal,  165 ;  types  of,  167 ;  high- 
est, 172. 

Mouths  of  cells,  220. 

Muck,  82. 

Mud,  cracks,  257;  flow,  257;  with 
volcanic  eruption,  138. 

Mural  System,  208. 


INDEX. 


505 


Murchison,  Sir  R.,  381. 
Murraysville  gas,  201. 
Muscovite,  80f;  associates  of,  55. 
Mussels,  82. 
Mylodon,  459. 
Myrmecobius  fasciatus,  346*. 

Nahant,  58,  99. 

Nanosaurus,  339. 

Naphtha,  69,  194. 

Natchez,  285. 

Nautiloidea,  328,  329. 

Nautilus,  326,  327*,  328,  402,  444. 

Navajo  Mt,  437. 

Nebraska,  438. 

Needles  in  mountains,  166*,  167*. 

Neocene,  441. 

Nesquehoning  Coal  Basin,  412*. 

Nevada,  184.  374,  376,  406;  Coal 
Measures,  410 ;  Jurassic,  428 ;  Ter- 
tiary, 443;  Quaternary,  453;  fos- 
sils, 379. 

Nevada  Land,  383,  400,  468,  472. 

Newberry,  J.  S.,  on  sand  action,  284. 

New  Brunswick,  184,  192,  386,  398. 

New  Buffalo  dunes,  285. 

New  Hampshire,  386. 

New  Jersey,  iron  in,  183,  184,  429, 
442,  448,  472;  subsiding,  487. 

New  Mexico,  lava  sheets,  154;  tin, 
185;  Cretaceous,  430,  431;  coal, 
432 ;  Tertiary,  443*. 

New  York,  69,  375,  376,  384,  385,  392, 
469;  rock  salt  in,  386. 

New  Zealand  hot  springs,  134. 

Niagara,  erosion,  89,  386,  488;  falls, 
89,  386,  387,  388*;  gorge,  388*; 
Group,  381;  Limestone,  197,  382, 
385,  391. 

Nitre  caves,  40. 

Norite,  53,  54,  366;  eruptive,  71. 

North  America,  geological  map  of, 
361. 

North  Carolina,  425. 

North,  the  source  of  bowlders,  15. 

North  pole,  habitability  of,  295. 

Norway,  iron  in,  183. 

Novaculite,  46,  61. 

Nova  Scotia,  48,  49,  192,  198,  386, 
398;  coal,  317. 

Novaya  Zemlia,  145. 

Obelisk  syenitic,  53. 


Oblateness  diminishing,  175,  299. 

Oblique  lamination,  256. 

Obsidian,  72. 

Occlusor  muscle,  231*. 

Ocean,  action  of,  279. 

Ocean  pressure  and  folds,  175. 

Ochre,  37. 

Ocoee  formations,  374. 

Odontolca3,  345. 

Odontornithes,  345. 

Odontotorma?,  345. 

Ohio,  iron  in,  183;  brine,  192;  oil, 
196;  gas,  201;  gypsum,  386;  coal, 
407,  416;  coal  section,  410;  forma- 
tions, 274,  370,  378,  384,  390,  391, 
392. 

Oil  Creek,  195. 

Oil  sands.    See  table,  403  seq. 

Oil  stone,  61. 

Old  Red  Sandstone,  390. 

Oligocene,  442. 

Oligoclase,  27. 

Olympic  mountains,  473. 

Omaha,  445. 

Onchus  Clintoni,  331. 

Oneida  Conglomerate,  381,  384. 

Onondaga  salines,  190;  Salt  Group, 
381. 

Ontario,  195;  petroleum,  196*,  197; 
fossils,  202;  rocks,  384,  392,  400; 
Erie  clays,  452. 

Ontario,  Lake,  88. 

Onychodus  sigmoides,  332*. 

Oolitic  limestone,  63. 

Ooze  in  Atlantic,  86. 

Opal,  303. 

Orange  county  mastodon,  457. 

Oregon  Quaternary  lakes,  453 ;  tuffs, 
478. 

Ores,  177  seq. 

Organic  and  inorganic,  247. 

Oriskany  Group,  390. 

Ornithipoda,  339. 

Ornithopterus,  343. 

Ornithotarsus  immanis,  340. 

Orohippus,  356. 

Orthis,  228,  241,  476;  biforata,  228* 
233,  380,  402;  subquadrata,  229*, 
232*,  380. 

Orthoceras,  restored,  327* ;  siphuncle 
of,  327*;  age  of,  328;  Carleyi, 
330*:  in  Cambrian,  380. 

Orthoclase,  26*,  27* ;  associates  of,  55. 


506 


INDEX. 


Orthoclinal  mountains,  167. 

Orton,  E.,  68;  on  Coal  Measures,  403. 

Osars,  447. 

Ostrea  larva,  423. 

Outcrop,  99,  100*,  260. 

Outlier,  264. 

Overflow  and  age,  266. 

Overlying,  100. 

Overturned  fold,  262. 

Owen,  R.,  340. 

Oxides,  19f ;  acid-forming  and  basic, 

19. 
Oxygen,  some  properties  of,  19. 

Palaeaspis,  331. 

Palaeontology,  246f. 

Palaaophycus  arthrophycus,  386*. 

Palaeozoic  ^Eon,  468. 

Palisades,  155. 

Palmyra  Lake,  85. 

Palpebral  lobe,  324. 

Pantodonta,  351. 

Pantotheria,  347. 

Paradoxides  Harlani,  323*. 

Paraffine,  69. 

Paragenesis,  180. 

Paria  fold  and  plateau,  164*. 

Parian  marble,  62. 

Park  Range,  163,  434,  468;  constitu- 
tion of,  436;  section  across,  437*. 

Parks  in  Rocky  Mountains,  434. 

Parma  Conglomerate,  192,  406. 

Parma  oil  region,  199. 

Parophite,  368. 

Pay  gravel,  152. 

Pearl  spar,  36. 

Pearl  stone,  72. 

Peat,  68,  82,  421. 

Pebble,  4f. 

Pen  of  Belemnite,  433. 

Pennsylvania,  iron,  183,  184,  194, 
196 ;  oil,  195  seq. ;  gas,  201 ;  coal, 
407,  416;  formations,  274,  391, 
398,  424;  fossils,  379;  Drift,  449. 

Pentacrinus,  428. 

Penokie  iron  range.  183*,  367. 

Pentelican  marble,  62. 

Peperino,  250. 

Perboewatan,  145. 

Perforation  in  beak,  235*. 

Period,  270. 

Peripheral  region  of  coral,  208. 

Perissodactyla,  351. 


Permian  Group,  402. 

Perrey  on  earthquakes,  298. 

Petite  Anse,  193. 

Petrifaction,  303. 

Petrography,  248. 

Petroleum,  68,  69;  geology  of,  194; 
laws  of  accumulation,  198;  con- 
spectus of,  199;  diagram,  200.* 

Petroliferous,  46,  250. 

Petrosilex,  57. 

Pharierocrystalline,  56,  251. 

Phaneropleuron,  333. 

Phascolotherium  Bucklandi,  346. 

Phenacodus,  349;  Wortmani,  350*. 

Phlogopite,  30. 

Phonolite,  72. 

Phragmocone,  433. 

Phyllite,  61. 

Physical  geography,  302. 

Pictured  Rocks,  373,  377. 

Pilot  Butte,  437. 

Pilot  Knob,  367. 

Pinnate  septa,  210. 

Pipestone,  363. 

Piroroco  of  Amazons,  280. 

Pisolitic  limestone,  63. 

Pitchstone,  72. 

Pittsburgh,  68;  gas  production,  201; 
coal  bed,  409. 

Placers,  152. 

Placoderms,  331. 

Placoganoids,  331. 

Plagiaulax,  347. 

Plagioclase,  27*;  discriminations,  28; 
as  rock-constituent,  366. 

Plagiostomes,  332. 

Plants  classified,  303;  Cretaceous, 
434,  475.  See  "Coal  Plants." 

Plaster  of  Paris,  36. 

Plastic  zone,  294. 

Plateau  Province,  434*,  441,  474; 
wastage  of,  92;  section  in,  164*; 
geology  of,  428,  436. 

Plates  of  crinoids,  325. 

Plesiosaurus  dolichodeirus,  337*. 

Plications  of  shell,  231*;  of  strata, 
263. 

Pliocene,  441 ;  inaugurated,  478, 
479. 

Pliohippus,  356. 

Plumbago,  67. 

Plunge,  angle  of,  260. 

Pluvial  epoch,  467. 


INDEX. 


507 


Pogonip  Limestone,  376. 

Polished  faces,  259. 

Polishing  action  of  sand,  284. 

Polyp,  214. 

Polypary,  203. 

Pompeii,  138,  140.* 

Porcelain  materials,  60. 

Porcupine  Mountains,  369. 

Pores  in  Favosites,  221. 

Pores  of  rocks  and  water  absorption, 

490. 

Porousness,  252. 
Porphyritic,  251 ;  felsite,  58;  granite, 

Porphyry,  251 ;  quartz,  58 ;  conglom- 
erate, 58;  Keweenian,  366;  intru- 
sions, 157;  silver  bearing,  184. 

Porphyry  bowlder,  14*. 

Portage  Stage,  389. 

Port  Hudson,  85. 

Port  Kennedy  cave,  457. 

Posterior  of  shell,  228. 

Potomac,  River,  81;  marble,  425. 

Potash  Kettles,  65,  450. 

Potsdam  Group,  369 ;  sandstone,  373, 
377. 

Powell,  J.  W.,  on  mountains,  161; 
Uintas,  162;  Colorado  plateau, 
165;  Cambrian,  370. 

Prairie,  2f. 

Precipitations,  293;  in  primitive 
ocean,  464. 

Preparation  of  sections  of  fossils, 
205. 

Presedirnentary  history,  463. 

Pressure,  lateral,  171,  172*,  291;  of 
glacier,  485. 

Primary  septa,  210*,  211*. 

Primordial  Group,  369. 

Priority,  laws  of,  272. 

Proboscidea,  351. 

Prochlorite,  31. 

Producta,  402. 

Profile,  geological,  125. 

Progress  in  life  history,  315. 

Protogine,  59. 

Protohippus,  356. 

Protorosaurus,  335. 

Protozoans,  position  of,  103. 

Protuberance  of  equator,  299f,  464. 

Provinces,  434f,  geology  of,  436. 

Prussia,  193,  194. 

Pseudamygdules,  264. 


Pseudodeltidium,  231,  237*,  239. 
Pseudomorph,  290. 
Pseudomorphism,  290. 
Pseudopodia,  319,  320. 
Pterichthys,  332,  333* ;    Canadensis, 

333. 

Pteridophytes,  418. 
Pterodactylus,     342 ;      crassirostris, 

341*. 

Pteropods,  86. 
Pterosauria,  342. 
Puerco,  443. 
Pumice,  72. 
Punctations,  238. 
Pyrenees,  193. 
Pyrite,  88,  303. 
Pyritous  rocks,  249. 
Pyrophyllite,  30,  60. 
Pyrophyllite  slate,  60. 
Pyroxene,  32. 
Pyroxenic  rocks,  52,  249. 
Pythonomorpha,  337. 

Quaquaversal  dip.  261. 

Quartz,  studied,  23. 

Quartzite,  45 ;  hornblendic,  52 ;  striat- 
ed, 283;  Baraboo,  363;  Prospect 
Mt.,  376;  Diamond  Park,  397; 
Wahsatch,440;  coal  measures,  409. 

Quartzose  rocks,  44  seq.,  249. 

Quebec  Stage,  369. 

Queen  Charlotte  Islands,  429. 

Quicklime,  21. 

Quincy  granite,  53. 

Radial  plates,  325. 

Rain,  with  volcanic  eruptions,  138; 
prints,  287.  ' 

Rains,  first,  464. 

Rakata  Mt.,  145. 

Range  of  fossils,  304;  organic  types, 
359. 

Rangoon  oil  region,  199. 

Ranier,  Mt.,  148. 

Ratitae,  316. 

Rays,  331. 

Reade,  J.  M.,  96. 

Recent  Epoch,  486. 

Recession  of  falls.  92. 

Red,  chalk,  37;  ochre  and  paint,  37. 
I   Red  sunsets,  145. 
I   Reef-building,  322. 
I   Re-fusing  of  crust,  465. 


508 


INDEX. 


Reign  of  Fishes,  335. 
Relief,  mountains  of,  161. 
Rensselaerite,  368. 

Reptiles,  position  of,  104,  316;  com- 
prehensive,  316;    descriptions  of, 

Resupinate,  241. 

Retardation  of  earth's  rotation,  299. 

Reticulating  stems,  223. 

Rhamphorhynchus,  342. 

Rhinoceros,  153. 

Rhizocrinus,  326;    Lofotensis,  324*. 

Rhode  Island  Coal  Field,  406. 

Rhornbohedron,  35. 

Rhyolite,  72. 

Richthofen  on  loss,  285. 

Rim-rock,  152. 

Ripidolite,  31. 

Ripple  marks,  257. 

Rochester,  N.  Y.,  88. 

Rock  cities,  407. 

Rock  salt,  385,  386. 

Rocks,   247,   248;    classification  of, 

107,  108,  115;   physical  conditions 

of,   248;    essential  and   accessory 

constituents,  248,  249. 
Rogers,  W.  B.,   on  Coal  Measures, 

402,  403. 

Rossie,  N.  Y.,  70. 
Rotten  Limestone,  429. 
Rugosa,  202  seq.;  table  of,  217. 
Ruined  cities,  407. 
Russel,  I.,  on  Quaternary  lakes,  453. 
Russia,  195. 

Saccharoidal,  62. 

Sacramento  River,  435. 

Saddles  of  septum,  330. 

Safford,  J.  M.,  on  Unaka  Mountains, 

160,  374;  Tennessee  geology,  374. 
Saginaw  River  brines,  192. 
Sahlite,  32. 
Saliferous  rocks.  249. 
Salina  Group,  381,  385. 
Salisbury  iron,  37. 
Salt,  geology  of,  186  seq.;  impurities 

of,  188. 

Salt  Lake  City,  53. 
Salts,  how  formed,  20;  how  named, 

20. 

San  Bernardino,  95. 
Sand,  250. 
Sand  blast  action,  259,  284. 


I    Sand  dunes,  285. 

Sandstone,  250. 

Sandusky,  65. 

Sandy  Hook,  456,  473. 

San  Francisco,  Mt.,  437. 

San  Mateo  Mountains,  154. 

Santa  Barbara,  198. 

Saskatchewan,  433. 

Savoy,  92. 

Scaly  minerals,  29. 

Scars  on  shells,  304;  on  tree-ferns, 
418. 

Scelidotherium,  459. 

Scenographic  results,  302. 

Scheererite,  69. 

Schist,  silicious,  46 ;  jaspery  and  ha3m- 
atitic,  46;  mica,  50;  granulite,  51; 
hornblende,  52.  184 ;  aphanitic, 
54;  sericite,  59;  protogine,  chlo- 
rite, talcose,  59;  chlorite,  84;  py- 
rophyllite,  argillaceous,  60;  haema- 
tite, magnetite,  jaspery,  69. 

Schistose,  16f. 

Schoharie  Grit,  390. 

Schuylkill  basin,  407;  section  across, 
412. 

Scotch  granite,  53. 

Scribner,  G.  H.,  on  north  pole,  296. 

Scrope  on  volcanoes,  148. 

Scrubgrass  Coal,  408. 

Seaboard  Land,  363,  372f,  399,  467, 
468,  472. 

Seams,  252*,  256. 

Sea  over  the  land,  101. 

Seattle,  432. 

Secret  Canon  Shale,  376. 

Section,  explained,  lllf,  112 ;  of 
earth's  crust,  115;  construction  of, 
from  map,  123  seq.;  Detroit  to 
Grand  Haven,  124*;  Ontario  to 
Pennsylvania,  126*;  Nashville  to 
Savannah,  128*;  through  Tennes- 
see, 93* ;  in  Appalachians,  94* ;  at 
Tuscan  Springs,  132*  ;  through 
Table  Mountains,  151*,  152*;  in 
Elba,  157* ;  through  laccolite,  157* ; 
Catskill  Mountains,  161*;  through 
Uinta  Mountains,  162*;  central 
Utah,  163*;  across  plateau  region, 
164*;  across  Appalachians,  170*; 
through  Alps,  172*;  through  Pe- 
nokie  range,  183* ;  Onondaga  sa- 
lines, 190*;  Michigan  basins,  191*; 


INDEX. 


509 


Ontario  oil  region,  196* ;  along  Ot- 
tawa River,  366 ;  along  upper  Mis- 
sissippi, 877* ;  in  undulating  Coal 
Measures,  410*  ;  Ohio  Measures, 
410;  Great  North  to  Little  North 
Mountain,  411;  across  Schuylkill 
basin,  412* ;  through  Alabama, 
430*;  across  Park  Province,  437*; 
aBonic,  480. 

Sections,  of  fossils,  205;  Zaphrentis 
prolifica,  206* ;  Amplexus  Yandelli, 
207*;  Heliophyllum  Halli,  213*, 
214*;  Cystiphyllurn  Americanum, 
215*  ;  Diphyphyllum  Archiaci, 
216*;  Favosites  Alpenensis,  221*; 
F.  nitella,  221*;  Alveolites  Gold- 
fussi,  223*;  Cladopora  Roameri, 
223*. 

Sedgwick,  Adam,  381. 

Sedimentary  rocks,  70. 

Sedimentation,  80f  seq.;  cycles  of, 
268,284. 

Seismic  phenomena,  292;  produced 
by  tidal  action,  298. 

Selachians,  402,  476. 

Selaginella,  419. 

Selenite,  36. 

Seneca  Lake,  88. 

Septa,  of  corals,  204,  206 ;  arrange- 
ment of,  210,  211*,  212*;  of  cham- 
bered shells,  326. 

Septal  system,  208. 

Serai  Conglomerate,  405. 

Sericite  schist,  59. 

Serpentine,  30,  184.  385. 

Servos,  92. 

Set,  of  gypsum,  36,  66. 

Sevier  Lake,  453. 

Sewanee  coal,  406. 

Shaft,  in  mining,  413,  414*. 

Shale,  argillaceous,  60;  bituminous, 
195. 

Shaly,  252. 

Shamokin  basin,  407. 

Sharks,  331,  402. 

Shasta,  Mt.,  47,  435. 

Shawnee  fault,  410. 

Sheets  of  lava,  150. 

Shi v wits  Plateau,  164*. 

Siam  hairy  elephant,  462. 

Siberian  elephant,  460,  461*. 

Sicily,  193. 

Siderite,  47,  70,  183. 


Sideritic  rocks,  249. 

Sierra  la  Sal,  437. 

Sierra  Nevada,  95,  435,  438,  473 ;  vol- 
canoes of,  147;  eruptions  from,  150; 
fault,  165. 

Sigillaria,  419*. 

Silica,  19,  25,  303. 

Silt  of  rivers,  277. 

Silurian,  life,  315,317;  System,  381. 

Silver,  184. 

Sink  holes,  65,  134. 

Sinking  sea  bottom,  294. 

Sinter,  silicious,  133,  136*. 

Sinus  in  Brachiopods,  228. 

Siphuncle  of  Cephalopods,  326,  237*. 

Sivatherium,  354. 

Skeleton,  supplementary,  320. 

Slate  pencils,  60. 

Slaty,  98;  structure,  258*. 

Sleeping  Bear,  284. 

Slopes  in  mining,  416. 

Smith,  E.  A.,  on  green  sand,  432. 

Soapstone.  59. 

Socket  of  hinge,  231*,  232.* 

Soil,  2f;  on  prairies,  2. 

Solenhofen  schists,  343. 

Solfatara,  140. 

Solubility,  252. 

Somma,  146. 

Soudan,  145. 

South  Carolina,  425,  479,  481. 

Spalacotheriurn,  347. 

Spanish  white,  64. 

Spar,  350. 

Sparry  rocks,  47. 

Spathic  iron,  70. 

Species  migrating,  102. 

Sperenberg  boring,  193. 

Spines  of  sharks,  332*. 

Spires  in  Brachiopods,  232*. 

Spirifera,  227,  241,402;  mucronata, 
227*,  229*,  231,  233*;  striata,  232*. 

Spiriferida3,  237. 

Spirigera,  228,  241 ;  spiriferoides. 
228*.  235*,  236*,  241. 

Split  Rock.  111.,  411. 

Sponges,  322. 

Spores  in  coal,  416. 

Springs  and  wells,  7  seq.,  8*. 

Springs,  thermal,  131*;  at  Sacra- 
mento Valley,  132*;  Clermont, 
132*;  National  Park,  133*. 

Squalodonts,  434,  444. 


510 


INDEX. 


Squeezing  together,  173. 

Stable,  138. 

Stage,  270. 

Stagonolepis,  335. 

Stains,  how  caused,  49. 

Stalactite,  64. 

Stalactitic  haematite,   37;  limonite, 

37. 

Stalagmite,  64. 
St.  Andre,  92. 
Star  Peak  Group,  424,  425. 
Stassfurt,  193. 
Statuary  marble,  62. 
Steam  eruptions,  289. 
Steatite,  59,  368. 
Stephanite,  184. 
Stereognathus,  346. 
Sterling,  70. 
Stevenson,  J.  J.,  on  Virginia  salt, 

192;  coal,  432. 

Stigmaria,  420*;  ficoides,  420*. 
St.  Ignace  bowlder,  14*. 
St.  John  formation,  362. 
St.  Louis'  stage,  395,  400,  401. 
St.  Paul's  cathedral,  64,  95. 
St.  Peter's  sandstones,  375. 
Stratification,  6,  16,  252f,  255. 
Stratigraphical    and    topographical, 

100. 
Stratum  and  Strata,  6,  97,  252f,  255, 

how  disposed,  108  seg.,  110*.     See 

"Sedimentation." 
Streak,  31*,  37. 
Streptelasma,  210,  217,  380;  cornicu- 

lum,  210.* 

Striation  by  glaciers,  283. 
Strike,  260. 

Stromatocerium  rugosum,  321. 
Stromatopora  tuberculata,  321;  stria- 

tella,  322. 

Stromatoporoids,  321,  322,  394. 
Strophomena,    230,    241,    380,   476; 

imequiradiata,    230*,   239*;    alter- 

nata,  239*. 

Structural  Geology,  246. 
Structure  of  crust  to  be  read  from 

map,  120,  123. 

Structure  of  rocks.  Table  of,  74. 
Stumps  in  coal.  417*. 
Stylacodon,  347. 
Stylodon,  347. 
Stylolites,  257. 
Styria,  70. 


Subcarboniferous,  395. 

Sublimation  in  veins,  291. 

Subsidence,  of  sea-bottom,  294;  dur- 
ing Coal  Measures,  412;  Cham- 
plain,  484. 

Subterf  usion  of  crust,  284*. 

Subterranean  waters.  277. 

Subvitreous  lustre,  25. 

Succession  of  organic  types,  105,  314; 
of  vertebrate  life,  357. 

Succinite,  68. 

Sugar  Loaf,  393. 

Sumatra,  200. 

Sump,  414*. 

Sun,  extinction  of,  296. 

Sundanese  volcanoes,  145,  146. 

Supercrust,  465. 

Superior,  Lake,  69,  71;  geology  of, 
466,  4.67. 

Superposition  and  age,  265,  266. 

Surface  materials,  1. 

Surprise  Valley,  453. 

Suture  of  Trilbbite,  324;  chambered 
shell,  327*. 

Syene,  52. 

Syenite,  52;  eruptive,  71;  quartz,  71. 

Sylvestri  on  jiEtna,  142. 

Symmetry,  bivalvular,  227;  univalvu- 
lar,  228. 

Synchronistic  motions,  490. 

Synclinal  basins,  110;  mountains, 
165*,  166*,  168;  axis,  261. 

Synclinorium,  294. 

Synonyms,  272. 

Syracuse,  brines  at,  188,  189,  190*. 

Syringothyris,  236,  241,  402;  tvpus, 
*236*,  237*. 

System,  270f. 


Table  mountains  in  California,  151*; 
in  Tuolumne  county,  152*;  in 
France,  153. 

Table  of,  chambered  shells,  329 ;  suc- 
cession of  life,  358;  composition 
of  minerals,  40-41;  determination 
of  minerals,  42-44;  standards  of 
hardness,  42;  rock-structure,  74; 
rock-composition,  75;  rock- deter- 
mination, 76-80;  Cup  Corals,  217; 
Tabulate  Corals.  224;  determina- 
tion of  Brachiopods,  240. 

Table  Rock,  387,  389*. 


INDEX. 


6118 


Tabula?  in  corals,  207;  in  Tabulate 
Corals,  220. 

Tabular  limestone  in  Drift,  451. 

Tabular  mountains,  168. 

Tabular  system  in  corals,  208. 

Tabulate  corals,  218  seq.,  401. 

Tacconay  glacier,  281. 

Taeniodonta,  350. 

Tails,  vertebrated,  of  birds,  317. 

Talc,  30. 

Talcose  rocks,  249. 

Taxeopoda,  350. 

Taylor  Mountain,  154. 

Teeth  of  Brachiopods,  229,  232*. 

Tejon  Group,  432. 

Teleosts,  331  f,  402,  444. 

Telerpeton,  335. 

Temescal,  95. 

Temperature  beneath  surface,  129. 

Tennessee,  65:  central  basin  of,  92*; 
valley  of  east,  92* ;  section  through, 
160,  161,  163;  iron  in,  184;  forma- 
tions, 370,  374,  378,  384,  396;  fos- 
sils, 379;  coal,  406,  416. 

Tentacles  of  molluscs,  326. 

Terebratula,  238;  Romingeri,  237*; 
flavescens,  238*. 

Terebratulida?,  237,  433. 

Terms  used  in  rock  classification, 
108. 

Terrace  formation,  441,  454. 

Terraces,  river,  278,  454. 

Terrane,  255. 

Tertiary, life, 3 16;  System,  441;  sub- 
divisions of,  444. 

Teton  Mountains,  374. 

Tetrabranchs,  326. 

Tetracoralla,  202,  475.  See  "Cup 
Corals." 

Texas,  429,  430,  474. 

Texture,  251;  granular,  45;  aphan- 
itic,  56. 

Theriodonta,  340. 

Thermal  waters,  129  seq. 

Thick-  and  thin-bedded,  16,  252. 

Thickened  strata  in  mountains,  293. 

Thickness,  calculation  of,  261. 

Three  Princes  vein.  180*. 

Thuringian  copper  slates,  184. 

Thylacotherium  Broderipii,  346* 

Tidal,  action,  297;  wave,  280. 

Tides,  high  primitive,  300. 

Till,  447. 


Tillodontia,  349,  350. 

Tillotherium  focliens,  349*. 

Time  and  events,  categories  of,  269.  % 

Time,  geological,  long,  106 ;  classifi- ' 
cation  of,  107,  108. 

Tinoceras,  351 ;  ingens,  352*. 

Tinodon,  347.  * 

Titanic  iron  ore,  69,  183. 

Toothed  structure,  257. 

Topographical  and   stratigraphical, 
100. 

Torbanite,  69. 

Toroweap  fault,  164*. 

Toughness,  251. 

Tourmaline,  32;  in  quartzite,  45;  in 
other  rocks,  52,  249. 

Trachyte,  72. 

Tracks  on  sandstone,  425*. 

Travertin,  64 ;  at  Clermont,  132. 

Tremolite,  31. 

Tremors  of  earth,  293. 

Trend,  260. 

Trenton  Group,  197,  369 ;  limestone, 
375. 

Triassic.  System,  424,  472,  438 ;  chan- 
nel of  Hudson  River,  455. 

Triclinic  feldspars,  27. 

Triconodon,  347. 

Trilobites,  323,  389,  421. 

Trinidad,  198. 

Tritylodon  longaBvus,  346. 

Tuckerman's  ravine,  483. 

Tufa,  11*,  64;  at  Clermont,  132*. 

Tuffs,  volcanic,  478. 

Tulare  Lake,  435. 

Tuluole,  69. 

Tuolumne  county,  152. 

Tuscany,  193. 

Tuscan  Springs,  132*,  150. 

Types  of  plants  and  animals,  305- 
314. 

Uinkaret  Mountains,  164*,  437. 
Uinta  Mountains,    162*,    165,    426, 

427,  428,  430,  431,  434,  440,  441. 
Uintatherium,  351,  353;  Leidyanum, 

351*;  mirabile,  351*. 
Ulterior  history,  488. 
Umbral  Series,'  398,  399. 
Unaka  Mountains,  93,  160,  374. 
Unconformability,  100. 
Underlying,  100. 
Ungulata,  351. 


INDEX. 


Jniformitarian  view,  456. 

Jnivalves,  82. 

Jnivalvular  symmetry,  227. 

Jnstratified  rocks,  264. 

Jpham,  W.,  on  Lake  Agassiz,  452. 

Jplifts,  101. 

Jpper    Carboniferous    System,    402 

seq. 

Jpper  Freeport  Coal,  408. 
Jpper  Mercer  Limeetone,  408. 
Jrocentrum,  319*, 
Jtah,  section  in,  163*,  165;  rocks  of, 

397,  406,  424,  437;   coal  in,  432; 

Lake,  453. 
Jtica  Stage,  369. 

Valve  of  shell,  226. 

Vancouver  Island,  429. 

Variations  from  type  to  type,  105. 

Variolite,  72. 

Vascular  impressions,  230*,  231,  232, 
304. 

Vegetation.     See  "Plants." 

Vein,  condition,  265 ;  filling  of,  296. 

Vein  intersections  and  age,  267. 

Veins,  mineral,  177*  seq. ;  quartzose, 
177,  178;  intersecting,  176;  kinds 
of,  181. 

Ventral  valve,  227. 

Verd  antique,  62. 

Vermont  marble,  62;  iron  ore,  70; 
rocks,  370. 

Vertebrated  tail,  335*. 

Vertebrates,  position  of,  104. 

Vertical,  force,  175;  range  of  fossils, 
304. 

Vesicle,  contracile,  319*. 

Vespertine  Series,  398,  399. 

Vesuvian  lava,  72. 

Vesuvius,  described,  138;  crater  of, 
138;  crater  of,  in  1756,  146*;  erup- 
tions of,  in  79  A.D.,  138;  in  1872 
139* 

Vicksburg,  85,  445. 

Victoria  coal,  433. 

Virginia,  65,  192,  398,  425. 

Visceral  cavity  of  coral,  207. 

Vitreous  lustre  of  quartz,  23. 

Vogt,  Carl,  344. 

Volanic,  outflows,  437;  tuffs,  478. 

Volcanoes,  138  seq. ;  extinct,  148. 

Wachsmuth.  C.,  on  crinoids,  401. 


Wad  manganese,  12. 

Wahsatch  Mountains,  160,  165,  374, 

397,  409,  426,  427,   428,  435,  440, 

443,    468,    474;     uprise    of,    438; 

formation,    476;    coal    measures, 

409. 

Waldheimia,  238. 
Walker  Lake,  453. 
Wall  of  a  coral,  204,  206. 
Walled  lakes,  15. 
Ward,  H.  A.,  on  mammoth,  461. 
Warren,  J.  C.,  mastodon,  459. 
Warren,  W.  F.,  on  north  pole,  296. 
Warm  water,  131. 
Warsaw  limestone,  401. 
Washakie  Basin,  477. 
Washington  Territory,  432,  473,  478. 
Water  as  a  dynamic  agent,  276. 
Waters    of    springs    and  wells,    10; 

often  impure,  11;  thermal,  131. 
Watertown,  N.  Y.,  376. 
Watkins'  Glen,  88*. 
Waugoshance  Point  bowlders,  15. 
Wave  action,  279. 
Waverly  sandstone,    192,   390,  396, 

402. 

Wave,  tidal,  280. 
Waxy  solids,  69. 
Weathering,  effects  of,  178. 
Weber  conglomerate. 
Wells,  9;  deep  and  shallow,  10*. 
Western  interior  Coal  Field,  406. 
West  Humboldt  Range,  426. 
West  Rock,  155. 
West  Virginia,  197. 
Whale  in  Lake  Champlain,  457. 
White,   C.  A.,  on  Cretaceous,  431, 

432. 

White  Limestone,  444. 
White  River,  443,  499. 
Whiting,  64. 
Whetstone,   49.     See  "  Novaculite, " 

46. 

White  Cliffs  Group,  424. 
Wielicza,  193. 

Winchell,  N.  H.,  on  Cambrian  fos- 
sils, 363. 

Windings  of  Mississippi,  84*. 
Wind  River  Mountains,  443 ;  valley, 

478. 

Windsor  series,  398. 
Winnemuca  Lake,  453. 
Winnipeg,  375,  485. 


INDEX. 


513 


Wisconsin,  95;  river,  89;  rocks,  365*, 

370, 376*,  384, 469 ;  quartzite,  374* ; 

fossils,  379 ;  moraine,  451*. 
Wortrnan,  J.  E.,  348. 
Wright,  G.  P.,  on  moraine,  448. 
Wrinkles,  172,  173;  how  caused,  174, 

464;    disposition     of,    173.      See 

"Folds." 
Wyoming,   185,  851,  397,  406,  428, 

478;  coal  in,  432. 
Wyoming  anthracite  basin,  407. 
Wyoming  county,  N.  Y.,  190. 
Wythe  county  caves,  457. 


Yazoo  River,  85. 
Yellow  ochre,  37. 

Yellowstone,    National    Park,    133, 
140 ;  River,  476. 


Zaphrentis,  204,  217 ;   prolifica,  204*, 

206*:  Ida,  212*. 
Zeuglodon,  444. 
Zinc  iron  ore,  69. 
Zoophytes,  324. 

Zygospira,  233,   241;    modesta,  233, 
'235*. 


OVERDUE. 


YC  3S80C 


QEiC. 

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